Author: Frank

GIS & Data Librarian at Brown University

Sample of Geolocated Tweets Nov 1, 2022

Parsing the Internet Archive’s Twitter Stream Grab with Python

In this post I’ll share a process for getting geo-located tweets from Twitter, using large files of tweets archived by the Internet Archive. These are tweets where the user opted to have their phone or device record the longitude and latitude coordinates for their location, at the time of the tweet. I’ve created some straightforward scripts in Python without any 3rd party modules for processing a daily file of tweets. Given all the turmoil at Twitter in early 2023, most of the tried and true solutions for scraping tweets or using their APIs no longer function. What I’m presenting here is one, simple solution.

Social media data is not my forte, as I specialize in working with official government datasets. When such questions turn up from students, I’ve always turned to the great Web Scraping Toolkit developed by our library’s Center for Digital Scholarship. But the graduate student I was helping last week and I discovered that both the Twint and TAGS tools no longer function due to changes in Twitter’s developer policies. Surely there must be another solution – there are millions of posts on the internet that show how easy it is to grab tweets via R or Python! Alas, we tried several alternatives to no avail. Many of these projects rely on third party modules that are deprecated or dodgy (or both), and even if you can escape from dependency hell and get everything working, the changed policies rendered them moot.

You can register under Twitter’s new API policy and get access to a paltry number of records. But I thought – surely, someone else has scraped tons of tweets for academic research purposes and has archived them somewhere – could we just access those? Indeed, the folks at Harvard have. They have an archive of geolocated tweets in their dataverse repository, and another one for political tweets. They are also affiliated with a much larger project called DocNow with other schools that have different tweet archives. But alas, there are rules to follow, and to comply with Twitter’s license agreement Harvard and these institutions can’t directly share the raw tweets with anyone outside their institutions. You can search and get IDs to the tweets, using their Hydrator application, which you can use in turn to get the actual tweets. But then in small print:

“Twitter’s changes to their API which greatly reduce the amount of read-only access means that the Hydrator is no longer a useful application. The application keys, which functioned for the last 7 years, have been rescinded by Twitter.”

Fortunately, there is the Internet Archive, which has been working to preserve pieces of the internet for posterity for several decades. Their Twitter Stream Grab consists of monthly collections of daily files for the past few years, from 2016 to 2022. This project is no longer active, but there’s a newer one called the Twitter Archiving Project which has data from 2017 to now. I didn’t investigate this latter one, because I wasn’t sure if it provided the actual tweets or just metadata about them, while the older project definitely did. The IA describes the Stream Grab as the “spritzer” version of Twitter grabs (as opposed to a sprinkler or garden hose). Thanks to the internet, it’s easy to find statistics but hard to find reliable ones – this one, credible looking source (the GDELT Project) suggests that there are between 400 and 500 million tweets a day in recent years. The file I downloaded from IA for one day had over 4 million tweets, so that’s about 1% of all tweets.

I went into the November 2022 collection and downloaded the file for Nov 1st. It’s a TAR file that’s about 3 GB. Unzipping it gives you a folder for that data named for the date, with hundreds of gz ZIP files. Unzip those, and you have tons of JSON Line files. These are JSON files where each JSON record has been collapsed into one line.

Internet Archive Twitter Stream Grab

Python to the rescue. See GitHub for the full scripts – I’ll just add some snippets here for illustration. I wrote two scripts: the first reads in and aggregates all the tweets from the JSONL files, parses them into a Python dictionary, and writes out the geo-located records into regular JSON. The second reads in that file, selects the elements and values that we want into a list format, and writes those out to a CSV. The rationale was to separate importing and parsing from making these selections, as we’re not going to want to repeat the time-consuming first part while we’re tweaking and modifying the second part.

In the sample data I used for 11/01/2022, unzipping the downloaded TAR file gave me a date folder, and in that date folder were hundreds of gz ZIP files. Unzipping those revealed the JSONL files. I wrote the script to look in that date folder, one level below the folder that holds the scripts, and read in anything that ended with .json. Not all of the Internet Archive’s stream’s are structured this way; if your downloads are structured differently, you can simply move all the unzipped json files to one directory below the script to read them. Or, you can modify the script to iterate through sub-directories.

Because the data was stored as JSONL, I wasn’t able to read it in as regular JSON. I read each line as a string that I appended to a list, iterated through that list to convert it into a dictionary, pulled out the records that had geo-located elements, and added those records to a larger dictionary where I used an identifier in the record as a key and the value as a dictionary with all elements and values for a tweet. This gets written out as regular JSON at the end. Reading the data in didn’t take long; parsing the strings into dictionaries was the time consuming part. Originally, I wanted to parse and save all 4 million records, but the process stalled around 750k as I ran out of memory. Since so few records are geo-located, just selecting these circumvented this problem. If you wanted to modify this part to get other kinds of records, you would need to apply some filter, or implement a more efficient process than what I’m using.

json_list=[] # list of lists, each sublist has 1 string element = 1 line

for f in os.listdir(json_dir):
    if f.endswith('.json'):
        json_file=os.path.join(json_dir,f)
        with open(json_file,'r',encoding='utf-8') as jf:
            jfile_list = list(jf) # create list with one element, a line saved as a string 
            json_list.extend(jfile_list)
            print('Processed file',f,'...')

geo_dict={} # dictionary of dicts, each dict has line parsed into keys / values
i=0   
for json_str in json_list:
    result = json.loads(json_str) # convert line / string to dict
    if result.get('geo')!=None: # only take records that were geocoded
        geo_dict[result['id']]=result 
    i=i+1
    if i%100000==0:
        print('Processed',i,'records...')

The second script reads the JSON output from the first, and simply iterates through the dictionary and chooses the elements and values I want and assigns them to variables. Some of these are straightforward, such as grabbing the timestamp and tweet. Others required additional work. The source element provides HTML code with a source link and name, so I split and strip this value to get them separately. The coordinates are stored as a list, so to get longitude and latitude as separate values I indicate the list position. In cases where I’m delving into a sub-dictionary to get a value (like the coordinates), I added if statements to set values to None if they don’t exist in the JSON, otherwise you get an error. Once I finish iterating, I append all these variables to a list, and add this list to the main one that captures every record. I create a matching header row list, and both are written out as a CSV.

with open(input_json) as json_file:
    twit_data = json.load(json_file)

twit_list=[]

# In this block, select just the keys / values to save
for k,v in twit_data.items():
    tweet_id=k
    timestamp=v.get('created_at')
    tweet=v.get('text')
    # Source is in HTML with anchors. Separate the link and source name
    source=v.get('source') # This is in HTML
    source_url=source.split('"')[1] # This gets the url
    source_name=source.strip('</a>').split('>')[-1] # This gets the name
    lang=v.get('lang')
    # Value for long / lat is stored in a list, must specify position
    if v['geo'] !=None:
        longitude=v.get('geo').get('coordinates')[1]
        latitude=v.get('geo').get('coordinates')[0]
    else:
        longitude=None
        latitude=None
...

My code could use improvement – much of this could be abstracted into a function to avoid repetition. We were in a hurry, and I’m also working with folks who need data but aren’t necessarily familiar with Python, so something that’s inefficient but understandable is okay (although I will polish this up in the future).

I provide the output in GitHub, examples of the final CSV appear below. Every language in the world is captured in these tweets, so Windows users need to import the CSV into Excel (Data – From Text/CSV) and choose UTF-8 encoding. Double-clicking the CSV to open it in Excel in Windows will render most of the text as junk, in the default Windows-1252 encoding.

Tweets extracted from Internet Archive with timestamp, tweets, and source information
Geolocated Twitter Data 1
Tweets extracted from Internet Archive, showing geo-located information

So, is this data actually useful? That’s an open question. Of the 4 million tweets in this file, just over 1,158 were geo-located! I checked and this is not a mistake. The metadata record for the Harvard geolocated tweets mentions that only 1% to 2% of all tweets are geo-located. So of the 400 million daily tweets, only 4 million. And out of our daily 4 million sample from IA, just 1,158 (less than 1%). What we ended up with does give you a sense of variety and global coverage (see map at the top of the post, showing sample of tweets by language Nov 1, 2022). In this sample, the top five countries represented were: US (35%), Japan (17%), Brazil (4%), UK (4%), Mexico and Turkey (tied 3%). For languages, the top five: English (51%), Japanese (17%), Spanish (9%), Portuguese (5%), and Turkish (3%).

In many cases, I think you’d need a larger sample than a single day, assuming you’re interested in just geo-located records. Perhaps 4 million is large enough for certain non-spatial research? Again, not my area of expertise, but you would want to be aware of events that happened on a certain date that would influence what was tweeted. My graduate student wanted to see differences in certain kinds of tweets in the LA metro area versus the rest of the US, but this sample includes less than 20 tweets from LA. To do anything meaningful, she’d have to download and process a whole month of tweets (at least). Even then, there are certain tweeters that show up repeatedly in given areas. In NYC, most of the tweets on this date were from the 511 service, warning people where that day’s potholes were.

Beyond the location of the tweet, there is a lot of information about the user, including their self-reported location. This data is available in all tweets (not just the geo-located ones). But there are a lot problems with this attribute: the user isn’t necessarily tweeting from that location, as it represents their “static” home. This location is not geocoded, and it’s self reported and uncontrolled. In this example, some users dutifully reported their home as ‘Cleveland, OH’ or ‘New York City’. Other folks listed ‘NYC – LA – ATL – MIA’, ‘CIUDAD DE LAS BAJAS PASIONES’, ‘H E L L’, and ‘Earth. For now’.

Even for research that incorporated geo-located tweets from other, larger data sources that were previously accessible, how representative are all those studies when the data represents only 1% of the total tweet volume? I am skeptical. Also consider the information from the good folks at the Pew Research Center, that tells us that only one in five US adults use Twitter, and that the minority of Twitter users generate the vast majority of tweets: “The top 25% of US users by tweet volume produce 97% of all tweets, while the bottom 75% of users produce just 3%” (10 Facts About Americans and Twitter May 5, 2022).

For what’s it worth, if you need access to Twitter data for academic, non-commercial research purposes and the old methods aren’t working, perhaps the Internet Archive’s data and the solution posed here will fit the bill. You can see the geo-located output (JSON and CSV) from this example in the GitHub repo’s output folder. There is also a samples folder, which contains JSON and CSV for about 77k records that include both geo-located and non-geolocated examples. Looking at the examples can help you decide how to modify the scripts, to pull out different elements and values of interest.

Raster Temperature Jan 1, 2020 Southern NE

Summarizing Raster Data for Areas and Assigning Values to Points

It’s been a busy few months, but I have a few days to catch my breath now that it’s spring break and most people (except me) have gone away! One question that’s come up quite a bit this semester is how to associate raster data with coinciding vector data. I’ll summarize some approaches in this post using ArcGIS Pro and QGIS, to summarize raster values for polygons (zonal statistics) and to assign raster values to points (aka raster sampling).

Zonal Statistics: Summarize Rasters by Area

Imagine that you have quantitative values such as temperature or a vegetation index in a raster grid, and you want to use this data to calculate an average for counties or metro areas. The goal is to have a new attribute column in the vector layer that contains the summarized raster value, perhaps because you want to make thematic maps of that value, or you want to use it in conjunction with other variables to run spatial statistics, or you just want a plain and simple summary for given places.

The term zonal statistics is used to define any operation that calculates statistics on cell values of a raster within an area or zone defined by another dataset, either a raster or a vector. The ArcGIS Pro toolbox has a Zonal Statistics tool where the output is a new raster file with cells that are summarized by the input zones. That’s not desirable for the use case I’m presenting here; the better choice is the Zonal Statistics as Table tool. The output is a table containing the unique identifiers of the raster and vector, the summary stats you’ve generated (average, sum, min, max, etc), and a count of the number of cells used to generate the summary. You can join this resulting table back to the vector file using their common unique identifier in a table join.

In the example below, I’m using counties from the census TIGER files for southern New England as my Input Feature Zone, the AFFGEOID (Census ANSI / FIPS code) to identify the Zone Field, and a temperature grid for January 1, 2020 from PRISM as the Input Value Raster. I’m calculating the mean temperature for the counties on that day.

ArcGIS Zonal Statistics as Table Tool
ArcGIS Pro Zonal Statistics as Table; Temperature Grid and Southern New England Counties

The output table consists of one record for each zone / county, with the count of the cells used to create the average, and the mean temperature (in degrees Celsius). This table can be joined back to the original vector feature (select the county feature in the Contents, right click, Joins and Relates – Join) to thematically map the average temp.

ArcGIS Zonal Statistics Result
ArcGIS Pro Zonal Statistics; Table Output and Join to Show Average Temperature per County

In QGIS, this tool is simply called Zonal Statistics; search for it in the Processing toolbox. The vector with the zones is the Input layer, and the Raster layer is the grid with the values. By default the summary stats are the count, sum, and mean, but you can check the Statistics to calculate box to select others. Unlike ArcGIS, QGIS allows you to write output as a table or a new shapefile / geopackage, which carries along the feature geometry from the Input zones and adds the summaries, allowing you to skip the step of having to do a table join (if you opted to create a table, you could join it to the zones using the Joins tab under the Properties menu for the vector features).

QGIS Zonal Stats
QGIS Zonal Statistics

Extract Raster Values for Point Features

Zonal stats allows you to summarize raster data within a polygon. But what if you had point features, and wanted to assign each point the value of the raster cell that it falls within? In ArcGIS Pro, search the toolbox for the Extract Values to Points tool. You select your input points and raster, and a new point feature that will include the raster values. The default is to take the value for the cell that the point falls within, but there is an Interpolate option that will calculate the value from adjacent cells. The output point feature contains a new column called RASTERVALU. I created some phony point data and used it to generate the output below.

ArcGIS Extract Values to Points
ArcGIS Pro Extract Values to Points (assign raster cell values to points)

In QGIS the name of this tool is Sample raster values, which you can find in the Processing toolbox. Input the points, choose a raster layer, and write the output to a new vector point file. Unlike ArcGIS, there isn’t an option for interpolation from surrounding cells; you simply get the value for the cell that the point falls within. If you needed to interpolate, you can go to the Plugins menu, enable the SAGA plugin, and in the Processing toolbox try the SAGA tool Raster Values to Points instead.

QGIS Sample Raster Values
QGIS Sample Raster Values (assign raster cell values to points)

A variation on this theme would be to create and assign an average value around each point at a given distance, such as the average temperature within five miles. One way to achieve this would be to use the buffer tools in either ArcGIS or QGIS to create distinct buffers around each point at the specified distance. The buffer will automatically carry over all the attributes from the point features, including unique identifiers. Then you can run the zonal statistics tools against the buffer polygons and raster to compute the average, and if need be do a table join between the output table and the original point layer using their common identifier.

Wrap-up

In using any of these tools, it’s important to consider the resolution of the raster (i.e. the size of the grid cell):

1. Relative to the size of the zonal areas or number of points, and

2. In relation to the phenomena that you’re studying.

When larger grid cells or zonal areas are used for measurement, any phenomena becomes more generalized, and any variations within these large areas become masked. The temperature grid cells in this example had a resolution of 2.5 miles, which was suitable for creating county summaries. Summarizing data for census tracts at this resolution would be less ideal, as the tracts are much smaller than the cells, with the cell value characterizing a much larger area. This might be okay in the case of temperature, which tends not to vary considerably over a distance of a few miles. In contrast, averaging temperature data for states is not worthwhile, as states vary considerably in size and most are large enough that they contain multiple ecosystems and elevation levels.

The solutions I’ve described here are the desktop GIS solutions. You could also use either spatial SQL in a geodatabase or a spatial extension in a scripting language like Python or R to perform similar operations. In both cases a basic overlay and intersection statement is used, in conjunction with some grouping function for calculating summaries. I’ve been doing a lot more spatial Python work with geopandas these past few months – perhaps a topic for a subsequent post…

Stata splash screen

Introduction to Stata Tutorial

This month’s post will be brief, but helpful for anyone who wants to learn Stata. I wrote a short tutorial called First Steps with Stata for an introductory social science data course I visited earlier this month. It’s intended for folks who have never used a statistical package or a command-driven interface, and represents initial steps prior to doing any statistical analysis:

  1. Loading and viewing Stata dta files
  2. Describing and summarizing data
  3. Modifying and recoding data
  4. Batch processing with Do files / scripts
  5. Importing data from other formats

I chose the data that I used in my examples to illustrate the difference between census microdata and summary data, using sample data from the Current Population Survey to illustrate the former, and a table from the American Community Survey to represent the latter.

I’m not a statistician by training; I know the basics but rely on Python, databases, Excel, or GIS packages instead of stats packages. I learned a bit of Stata on my own in order to maintain some datasets I’m responsible for hosting, but to prepare more comprehensively to write this tutorial I relied on Using Stata for Quantitative Analysis, which I highly recommend. There’s also an excellent collection of Stata learning modules created by UCLA’s Advance Research Computing Center. Stata’s official user documentation is second to none for clearly introducing and explaining the individual commands and syntax.

In my years working in higher ed, the social science and public policy faculty I’ve met have all sworn by Stata over the alternatives. A study of citations in the health sciences, where stats packages used for the research were referenced in the texts, illustrates that SPSS is employed most often, but that Stata and R have increased in importance / usage over the last twenty years, while SAS has declined. I’ve had some students tell me that Stata commands remind them of R. In searching through the numerous shallow reviews and comparisons on the web, I found this post from a data science company that compares R, Python, SPSS, SAS, and Stata to be comprehensive and even-handed in summarizing the strengths and weaknesses of each. In short, I thought Stata was fairly intuitive, and the ability to batch script commands in Do files and to capture all input / output in logs makes it particularity appealing for creating reproducible research. It’s also more affordable than the other proprietary stats packages and runs on all operating systems.

Example – print the first five records of the active dataset to the screen for specific variables:

list statefip age sex race cinethp in f/5
     +-------------------------------------------+
     | statefip   age      sex    race   cinethp |
     |-------------------------------------------|
  1. |  alabama    76   female   white       yes |
  2. |  alabama    68   female   black       yes |
  3. |  alabama    24     male   black        no |
  4. |  alabama    56   female   black        no |
  5. |  alabama    80   female   white       yes |
     |-------------------------------------------|
Project Linework Wargames

Snazzy Thematic Maps with Project Linework

When I’m making global thematic maps, I usually turn to Natural Earth. They provide country polygons and boundary lines, as well as features like cities and rivers, at several different scales. I always reference it in workshops that I teach, including the 2-week GIS Institute that I participated in earlier this month. It’s a solid, free data source and a good example for illustrating how scale and generalization work in cartography. It’s a “natural choice”, as they provide boundaries that depict the way the world actually looks.

I also discussed aesthetics and map design during the Institute. What if you don’t necessarily care about representing the boundaries exactly the way they are? If you rely on the map reader’s knowledge of the relative shape of the countries and their position on the globe, and you employ good labeling, you can choose boundaries that are more artistic and fun (provided that your only goal is making a basic thematic map and it’s not being published in a stodgy journal).

Project Linework is part of Something About Maps, an excellent blog by Daniel Huffman. The project consists of different series of public domain boundary files that have been generalized to provide interesting and visually attractive alternatives to standard features. The gallery contains a sample image and brief description of each series, including details on geographic coverage. Most of the series cover just North America or select portions of the world.

The three I’ll mention below are global in coverage. They come in shapefile and geojson formats, are projected in World Gall Stereographic (ESRI 54016), and include line and polygon coverages. The attribute tables have fields for ISO country codes, which are standard unique identifiers that allow for table joins for thematic mapping. I took my map of Wheat and Meslin Exports from Ukraine from an earlier post to create the following examples.

With the Wargames series, the world has been rendered using the little hexagon grids familiar to many war board gamers, and plenty of non-war gamers for that matter (think Settlers of Catan). Hexes are a an alternative to grids for determining adjacency.

Project Lineworks Map - Wargames
Project Linework: Wargames

Moriarty Hand is a more whimsical interpretation. It was drawn by hand by tracing line work from Natural Earth. The end result is more organic compared to Wargames. It comes in two scales, small and large (with an example of the latter below):

Project Lineworks Map - Moriarty Hand
Project Linework: Moriarty Hand

My personal favorite is 1981. It’s inspired by the basic polygon shapes that you would have seen in early computer graphics. When I was little I remember loading a DOS-based atlas program from a floppy disk, and slowly panning across a CGA monochrome screen as the machine chunked away to render countries that looked like these. Good if you’re looking for a retro vibe.

Project Lineworks Map - 1981
Project Linework: 1981

Happy mapping! Also from Something About Maps, check out this excellent poster and related post about families of map projections.

Dingo Paths from ZoaTrack

Wildlife Tracking GIS Data Sources

I’ve also received a number of questions this semester about animal observation and tracking data. Since I usually study people and not animals, I was a bit out of my element and had some homework to do. If you’ve ever watched nature shows, you’ve seen scientists tagging animals with collars or bands to track them by radio or satellite, or setting up cameras to record them. Many scientists upload their GPS coordinate data into publicly accessible repositories for others to download and use.

I’ve written a short, three-part document that I’ve posted on our tutorials page: GIS Data Sources for Wildlife Tutorial. In the first part, I provide summaries, links, and guidance on using large portals like Movebank and Zoatrack that include many species from all over the world (wild and domestic), as well a government repositories including NOAA’s National Center for Environment Information Geoportal and the National Park Service’s Data Store. The second part focuses on search strategies, crawling the web and combing through academic literature in library databases to find additional data. Since these datasets are highly diffuse, it’s worth going beyond the portals to see what else you can discover.

I describe how you can add and visualize this data in QGIS and ArcGIS Pro in the third and final part. Wildlife data comes packaged in a number of formats; in some cases you’ll find shapefiles or geodatabases that you can readily add and visualize, but more often than not the data is packaged in a plain CSV / TXT format. This requires you to plot the coordinates (X for longitude, Y for latitude) to create a dot map of the observations. Data files will often contain a number of individual animals, which can be uniquely identified with a tag ID, allowing you to symbolize the points by category so you have a different color or symbol for each individual. Alternatively, there might be separate data files for each individual, that you could add and symbolize differently. The files will contain either a sequential integer or a timestamp that indicates the order of the observations. With one field that indicates the order and another that identifies each individual, you can use a Points to Line or Points to Path tool to generate lines (tracks or trajectories) from the points (observations or detections).

You can see where dingos in Queensland, Australia are going in the screenshot below, which displays individual observation points, and the screenshot in the header of this post where the points were connected to form paths. I obtained the data from ZoaTrack and used QGIS for mapping. Check out the tutorial for details on how to find and map your favorite animals.

Dingo observations from ZoaTrack plotted in QGIS
Map of Ukraine Wheat Exports in 2021

Import and Export Data for Countries: Grain from Ukraine

I’ve been receiving more questions about geospatial data sources as the semester draws to a close. I’ll describe some sources that I haven’t used extensively before in the next couple of posts, beginning with data on bilateral trade: imports and exports between countries. We’ll look at the IMF’s Direction of Trade Statistics (DOTS) and the UN’s COMTRADE database. Both sources provide web-based portals, APIs, and bulk downloading. I’ll focus on the portals.

IMF Direction of Trade Statistics

IMF DOTS provides monthly, quarterly, and annual import and export data, represented as total dollar values for all goods exchanged. The annual data goes back to 1947, while the monthly / quarterly data goes back to 1960. All countries that are part of the IMF are included, plus a few others. Data for exports are published on a Free and On Board (FOB) price basis, while imports are published on a Cost, Insurance, Freight (CIF) price basis. Here are definitions for each term, quoted directly from the OECD’s Statistical Glossary:

The f.o.b. price (free on board price) of exports and imports of goods is the market value of the goods at the point of uniform valuation, (the customs frontier of the economy from which they are exported). It is equal to the c.i.f. price less the costs of transportation and insurance charges, between the customs frontier of the exporting (importing) country and that of the importing (exporting) country.

The c.i.f. price (i.e. cost, insurance and freight price) is the price of a good delivered at the frontier of the importing country, including any insurance and freight charges incurred to that point, or the price of a service delivered to a resident, before the payment of any import duties or other taxes on imports or trade and transport margins within the country.

OECD Glossary of Statistical Terms

There are a few different ways to browse and search for data. Start with the Data Tables tab at the top, and Exports and Imports by Areas and Countries. The default table displays monthly exports by region and country for the entire world (you could switch to imports by selecting the Imports CIF tab beside the Export sFOB tab). Hitting the Calendar dropdown allows you to change the date range and frequency. Hitting the Country dropdown lets you select a specific region or country. In the example below, I’ve changed the calendar from months to years, and the country to Ukraine. By doing so, the table now depicts the total US dollar value of exports and imports between Ukraine and all other countries. The Export button at the top allows you to save the report in a number of formats, Excel being the most data friendly option.

IMF DOTS Basic Report – Total Value of Exports from Ukraine, Last Five Years

While this is the quickest option, it comes with some downsides; the biggest one is that there are no unique identifiers for the countries, which is important if you wanted to join this table to a GIS vector file for mapping, or another country-level table in a database.

A better approach is to return to the home page and use the Query tab, which allows you to get a unique identifier and filter out countries and regions that are not of interest.

DOTS Query Tab
  1. Under Columns, select the time frame and interval. For example, check Years for Frequency at the top, and change the dropdowns at the bottom from Months to Years. From -5 to 0 would give you the last five years in ascending order.
  2. Rows allows you to filter out countries or regions that you don’t want to see in the results. You can also change the attribute that is displayed. Once the menu is open, right click in an empty area and choose Attribute. Here you can choose a variant country name, or an ISO country code. ISO codes are commonly used for uniquely identifying countries.
  3. Indicator lets you choose Exports (FOB), Imports (CIF or FOB), or Trade Balance, all in US dollars.
  4. Counterpart country is the country or region that you want to show trade for, such as Ukraine in our previous example.
  5. The tabs along the top allow you to produce graphs instead of a table (View – Table), to pivot the table (Adjust), and calculate summaries like sums or averages (Advanced).
  6. Export to produce an Excel file. By choosing the ISO codes you’ll lose the country names, but you can join the result to another country data table or shapefile and grab the names from there.
Modify Time
Modify Rows – Country – Change Attribute
DOTS Modified Table to Export: Total Value of Exports from Ukraine Last Five Years

UN COMTRADE

If you want data on the exchange of specific goods and services, quantities in addition to dollar values, and exchanges beyond simple imports and exports, then the UN’s COMTRADE database will be your source. You need to register to download data, but you can generate previews without having to log in. There is an extensive wiki that describes how to use the different database tools, and summaries of technical terms that you need to know for extracting and interpreting the data. You’ll need some understanding of the different systems for classifying commodities and goods. Your options (the links that follow lead to documentation and code lists) are: the Harmonized Classification System (HC), the Standard Industrial Trade Classification (SITC), and the Broad Economic Categories (BEC). What’s the difference? Here are some summaries, quoted directly from a UN report on the BEC:

The HS classification is maintained by the World Customs Organization. Its main purpose is to classify goods crossing the border for import tariffs or for application of some non-tariff measures for safety or health reasons. The HS classification is revised on a five-year cycle (p. 18)

The original SITC was designed in the 1950s as a tool for collection and dissemination of international merchandise trade statistics that would help in establishing internationally comparable trade statistics. By its introduction in 1988, the HS took over as collection and dissemination tool, and SITC was thereon used mostly as an analytical tool. (p. 19)

The Classification by Broad Economic Categories (BEC) is an international product classification. Its main purpose is to provide a set of broad product categories for the analysis of trade statistics. Since its adoption in 1971, statistical offices around the world have used BEC to report trade statistics in a concise and meaningful way (p. iii). The broad economic categories of BEC include all subheadings of the HS classification. Therefore, the total trade in terms of HS equals the total trade of the goods side of BEC. (p. 18)

Classification of Broad Economic Categories Rev 5 (2018)

In short, go with the BEC if you’re interested in high-level groupings, or the HS if you need detailed subdivisions. The SITC would be useful if you need to go further back in time, or if it facilitates looking at certain subdivisions or groupings that the other systems don’t capture.

From COMTRADE’s homepage, I suggest leaving the defaults in place and doing a basic, preliminary search for all global exports for the most recent year, so you can see basic output on the next screen. Then you can apply filters for a narrower search.

For example, let’s look at annual exports of wheat from Ukraine to other countries. Under the HS filter, remove the TOTAL code. Start typing wheat, and you’ll see various product categories: 6-digit codes are the most specific, while 4-digit codes are broader groups that encapsulate the 6-digit categories. We’ll choose wheat and meslin 1001. We’ll select Ukraine as the Reporter (the country that supplied the statistics and represents the origin point), and for the 1st partner we’ll choose All to get a list of all countries that Ukraine exported wheat to. The 2nd partner country we’ll leave as World (alternatively, you would add specific countries here if you wanted to know if there were intermediary nations between the origin and destination).

UN COMTARDE Refine Search with Filters

Hit Preview to see the results. You can click on a heading to sort by dollar value, weight, or country name. Like IMF DOTS, UN COMTRADE measures dollar amounts of exports as FOB and imports as CIF. At this point, you would need to log in to download the data as a CSV (creating an account is free). You would also need to be logged in if you generated an extract that has more than 500 records, otherwise the results will be truncated. You could always copy and paste data for shorter extracts directly from the screen to a spreadsheet, but you wouldn’t get any of the extra metadata fields that come with download, like ISO Country Codes and the classification codes for goods and merchandise.

COMTRADE Filtered Results – Exports of Wheat and Meslin from Ukraine 2021
Data Exported from COMTRADE to CSV with Identifiers

Mapping

For data from either source, if you wanted to map it you’d need to have a data table where there is one row for each country with columns of attributes, and with one column that has the ISO country code to serve as a unique identifier. Save the data table in an Excel file or as a table in a database. Download a country shapefile from Natural Earth. Add the shapefile and data table to a project and join them using the ISO code. Natural Earth shapefiles have several different ISO code columns that represent nations, sovereigns, and parent – child relationships; be sure you select the right one. Data table records that represent regions or groupings of countries (i.e. the EU, ASEAN, sum of smaller countries per continent not enumerated, etc.) will fall out of the dataset, as they won’t have a matching feature in the country shapefile. The map at the top of this post was created in QGIS, using COMTRADE and Natural Earth.