history

Philadelphia Redlining Map

Redlining Maps for GIS

I received several questions during the spring semester about redlining maps; where to find them, and how many were made. Known officially as Residential Security Maps, they were created by the Home Owners Loan Corporation in the 1930s to grade the level of security or risk for making home loans in residential portions of urban areas throughout the US. This New Deal program was intended to help people refinance mortgages and prevent foreclosures, while increasing buying opportunities to expand home ownership.

Areas were evaluated by lenders, developers, and appraisers and graded from A to D to indicate their desirability or risk level. Grade A was best (green), B still desirable (blue), C definitely declining (yellow), and D hazardous (red). The yellow and red areas were primarily populated by minorities, immigrants, and low income groups, and current research suggests that this program had a long reaching negative impact by enforcing and cementing segregation, disinvestment, and poverty in these areas.

The definitive digital source for these maps is the Mapping Inequality : Redlining in New Deal America project created at the University of Richmond’s Digital Scholarship Lab. They provide a solid history and summary of these maps and a good bibliography. The main portal is an interactive map of the US that allows you to zoom in and preview maps in different cities. You can click on individually zoned areas and get the original assessor or evaluator’s notes (when available). If you switch to the Downloads page you get a list of maps sorted alphabetically by state and city that you can download as: a jpeg of the original scanned map, a georeferenced image that can be added to GIS software as a raster, and a GIS vector polygon file (shapefile or geojson). In many cases there is also a scanned copy of the evaluators description and notes. You also have the option for downloading a unified vector file for the entire US as a shapefile or geojson. All of the data is provided under a Creative Commons Attribution Sharealike License.

Providence Redlining Map
Redlining Map of Providence, RI with graded areas, from the Mapping Inequality Project

There are a few other sources to choose from, but none of them are as complete. I originally thought of the National Archives which I thought would be the likely holder of the original paper maps, but only a fraction have been digitized. The PolicyMap database has most (but not all) of the maps available as a feature you can overlay in their platform. If you’re doing a basic web search this Slate article is among the first resources you’ll encounter, but most of the links are broken (which says something about the ephemeral nature of these kinds of digital projects).

How many maps were made? Amy Hillier’s work was among the earlier studies that examined these maps, and her case study of Philadelphia includes a detailed summary of the history of the HOLC program with references to primary source material. According to her research, 239 of these maps were made and she provides a list of each of the cities in the appendix. I was trying to discover how many maps were available in Rhode Island and found this list wasn’t complete; it only included Providence, while the Mapping Inequality project has maps for Providence, Pawtucket & Central Falls, and Woonsocket. I counted 202 maps based on unique names on Mapping Inequality, but some several individual maps include multiple cities.

She mentions that a population of 40,000 people was used as a cut-off for deciding which places to map, but noted that there were exceptions; Washington DC was omitted entirely, while there are several maps for urban counties in New Jersey as opposed to cities. In some case cities that were below the 40k threshold that were located beside larger ones were included. I checked the 1930 census against the three cities in Rhode Island that had maps, and indeed they were the only RI cities at that time that had more than 40k people (Central Falls had less than 40k but was included with Pawtucket as they’re adjacent). So this seemed to provide reasonable assurance that these were the only ones in existence for RI.

Finding the population data for the cities was another surprise. I had assumed this data was available in the NHGIS, but it wasn’t. The NHGIS includes data for places (Census Places) back to the 1970 census, which was the beginning of the period where a formal, bounded census place geography existed. Prior to this time, the Census Bureau published population count data for cities using other means, and the NHGIS is still working to include this information. It does exist (as you can find it in Wikipedia articles for most major cities) but is buried in old PDF reports on the Census Bureau’s website.

If you’re interested in learning more about the redlining maps beyond the documentation provided by Mapping Inequality, these articles provide detailed overviews of the HOLC and the residential security maps program, as well as their implications to the present day. You’ll need to access them through a library database:

Hillier, A.E. (2005). “Residential Security Maps and Neighborhood Appraisals: The Home Owners’ Loan Corporation and the Case of Philadelphia.” Social Science History, 29(2): 207-233.

Greer, J. (2012). “The Home Owners’ Loan Corporation and the Development of the Residential Security Maps“. Journal of Urban History, 39(2): 275-296.

CEC North America LULC

Dataset Roundup: A Summary of Specialized Open Data Sources

I list the top free GIS data sources that I consistently use on my Resources page; these are general, foundational sources that can be used for many applications. In this post I’m going to summarize an eclectic mix of more specialized resources that I’ve used or that have been recommended to me over this past year. I’ve categorized these into GIS datasets, sub-national population data for countries (tabular data that can be joined to GIS vector layers), and historic socio-economic data for countries.

Geospatial Data

North American Land Change Monitoring System

Published by the Commission for Environmental Cooperation, these land use and land cover rasters (see photo at the top of this post) are derived from MODIS imagery at 250 meter resolution for earlier years and either Landsat-7 or RapidEye imagery at 30 meter resolution for later years for Canada, the United States, and Mexico in 2005, 2010, and 2015. There are layers for both land cover and land cover change over a 5-year period. Land cover is classified into 19 categories based on UN FAO standards. It’s easy to download as the layer is unified (no individual tiles to mess with and stitch together) and for the 2015 series you can choose a national file or one for the entire continent.

PRISM Climate Data

Published by the Northwest Alliance for Computational Science & Engineering at Oregon State University, the PRISM Climate Group publishes climate data for the United States. You can generate daily, monthly, or 30-year normal rasters for temperature (min, max, mean), precipitation, dew point, and a few other measures for the continental US. There are also some prepackaged files that were created for special projects that cover Alaska, Hawaii, and some of the US territories. The site is very easy to use (certainly compared to other sites that provide climate data) and beyond its research applications the data is good for teaching purposes, as files are straightforward to create, download, and interpret.

PRISM Mean Temp Map Oct 2020

Marineregions.org Marine Boundaries

I usually help people find vector boundaries for terrestrial features, and the oceans are an afterthought that appear as the absence of land. But what if you specifically needed features that represent oceans and seas? Marineregions.org, maintained by the Flanders Marine Institute, provides many sets of water-based boundaries that include maritime regions (legal sea zones around countries) as well as polygons that represent the boundaries of the oceans and largest seas (IHO Sea Areas, defined by the International Hydrographic Association). See the screenshot of this layer in QGIS below.

IHO Seas Layer in QGIS

GNSS Time Series

Produced by NASA JPL, this dataset can be used for measuring vertical land movement (VLM) and subsistence, primarily due to movement of the earth’s tectonic plates. The dataset contains over 2,000 GPS observation points or stations; the majority are in the US but there are a scattering of points throughout the world. The data file for geodetic positions and velocities contains two records for every station: the POS (position) record provides data for the latitude (N), longitude (E), and elevation (V) in mm. The VEL (velocity) indicates the rate of movement over the time period by direction (N / E) and elevation. The last three columns for both sets of records are margins of error for each value. The data file is in a fixed-width text format. To use it in GIS you need to parse the data into a tabular format and drop the header information. When plotting the coordinates, the CRS for the geodetic file is IGS14 (EPSG code 9019). If your CRS library doesn’t include this system, it is roughly equivalent to ITRF2014 (EPSG code 7789).

Subnational Population Data

IPUMS Terra

Are you looking for population or socio-economic data for the first-level administrative divisions (states, provinces, departments, districts, etc) for many different countries? IPUMS Terra is part of the IPUMS series at the Minnesota Population Center, Univ of Minnesota. The data has been gathered from census and statistical agencies of individual countries, or in some cases from estimates generated by the project. Choose the "Create Your Custom Dataset" option, then on the next screen choose "Start Extract Area Level Output". On the Extract Builder (see pic below) choose variables on the left, like Demographic and Total Population. Then under Datasets on the right you can choose countries and filter by year. Once you move on to the next screen, you can choose to harmonize the output or choose specific years, and choose your administrative level: national, ADM-1, or smallest available. You must register to use the IPUMS data series, but registration is free for educational and non-commercial use (as long as you cite IPUMS as the source).

IPUMS Terra Interface

Subnational Human Development Index

An alternative for first-level admin data is the Subnational Human Development Index published by the GlobalDataLab at the Institute for Management Research at Radboud University. There are far fewer variables and less customization compared to IPUMS Terra, but as such the site is smaller and easier to use. There are several different indices for measuring human development, but you can also access the following indicators: life expectancy, GNI per capita, expected and mean years of schooling, and population size in millions.

Historic Global Population and Economic Data

Maddison Project

Yes, that’s Maddison with two "ds". This project from the Groningen Growth and Development Centre at the University of Groningen generates comparative economic growth, income, and population data for countries over a long historical time span; back to the year AD 1 in a few cases, but for the most part from AD 1500 forward. They provide detailed documentation that explains how the dataset was created, and it’s easy to download in either an Excel or STATA format.

The World Countries Urban Population

This dataset consists of two spreadsheet files – one for the total urban population and another for the urban ratio of the population for countries going back to the year 1500. The dataset was created by Jonathan Fink-Jensen at Utrecht University and is held in the International Institute of Social History’s data repository. The repository contains a variety of other historic socio-economic datasets for many different countries.