PUMAs and Mini-PUMAs in the 1960 5% Sample
For the 1960 5% sample, IPUMS has defined 1960 Public Use Microdata Areas (PUMAs), each having at least 100,000 residents, and mini-PUMAs, each having at least 50,000 residents. Codes for these areas are given by the PUMA and PUMAMINI variables. This page provides links to maps, relationship files, and boundary files for these areas, followed by complete documentation of the process and guidelines IPUMS used to create them.
- Relationship between tracts, PUMAs, and mini-PUMAs (.xlsx)
- Relationship between 2000 PUMAs and 1960 PUMAs (.xlsx)
All boundary files are provided as shapefiles within .ZIP files.
Creation Process and Guidelines
One of the primary goals of the IPUMS 1960 Data Restoration Project was the creation of new geographic areas modeled on Public Use Microdata Areas (PUMAs), the smallest identifiable geographic areas in modern public-use microdata. Along with the standard PUMA geographic level, the IPUMS-USA data restoration project created "mini-PUMAs" with a population threshold of 50,000 as opposed to the standard 100,000 population threshold. These mini-PUMAs nest within the standard PUMAs.
The process for creating these new geographies involved four phases. First, we created the input units using 1960 census tracts and counties from the National Historical Geographic Information System (NHGIS) (Minnesota Population Center 2011). Second, we created 1960-based approximations of 5%-sample 2000 PUMA boundaries. This allows users to compare consistent geographic units in 1960 and 2000. Third, we took all the 1960-based approximations of 2000 PUMAs that exceeded 100,000 people and subdivided them into mini-PUMAs, which still exceeded the 50,000-person threshold. Finally, we altered the mini-PUMA boundaries where necessary and appropriate to match the boundaries of Universal Area Codes, a geographic coding system unique to the 1960 census.
Creating Input Units
The first phase in the process was to construct the input geographic units. We started with the 1960 census tract and county shapefiles and the corresponding total population counts from the NHGIS. The NHGIS delineated census tract and county boundaries as defined for the 1960 Census of Population and Housing, and it obtained population data from Interuniversity Consortium for Political and Social Research (2000, 2005, 2007). We joined the population data to the shapefiles, and then we unioned the census tract and county shapefiles together. Since census tracts were not defined in all parts of the country, this unioned shapefile exhaustively covered the entire United States.
Our next step was to adjust the population totals for counties that were partially tracted in 1960. For all tracted counties, we summed the populations of the tracts and subtracted that total from the county population. We assigned that different difference to the county remainder polygon.
Creating 1960 PUMAs
The second phase of the process was creating Public Use Microdata Areas (PUMAs) from the 1960 input units. Our initial goal was to create 1960 PUMAs that aligned with 2000 PUMAs, which would allow users to compare consistent geographic units over time.
As a first step we created spatial approximations of 2000 PUMAs from the 1960 input units (tract, counties, and county remainders). To create the spatial approximations involved we carried out the following procedures:
- Unioned the 1960 input units with the 2000 PUMAs using a 10 meter tolerance to minimize sliver polygons.
- For each 1960 input unit, identified the 2000 PUMA with which it shared the largest area of overlap (plurality area).
- Assigned the 2000 PUMA code identified in (2) to the 1960 input unit.
- Dissolved the 1960 input units on that 2000 PUMA code to create 1960-based approximations of 2000 PUMAs. During the dissolve, we summed the population of the 1960 input units to yield the 1960 population of the 1960-based approximations of 2000 PUMAs.
This first step provides us with the three necessary pieces of information required to create 1960 PUMAs: the 1960-based approximations of 2000 PUMAs, the 1960-based populations for the approximations, and the 2000 PUMAs. In total we created 1,345 1960 PUMAs that matched 2000 PUMAs.
Creating 1960 Mini-PUMAs
This phase created units we call mini-PUMAs. These are geographic units that nest within 1960 PUMAs and have a minimum population of 50,000. Many of 1960 PUMAs created in the second phase had populations greater than 100,000. Thus, we sought to subdivide those PUMAs, where feasible, into mini-PUMAs.
We used Python, ArcGIS, and REDCAP to create the mini-PUMAs. REDCAP is a software program that aggregates spatial units into spatially continuous regions while optimizing an objective function (Guo 2008). We used the Ward's method for agglomerative clustering with a Rook contiguity constraint, set the minimum population for an output region to 50,000 people, and used population density for the objective function. Thus, REDCAP minimized the within-region population density and maximized the between-region population density, and it created output regions with a minimum population of 50,000 people.
Inter-university Consortium for Political and Social Research. Historical, Demographic, Economic, and Social Data: The United States, 1790-1970. ICPSR00003-v1. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 197. http://doi.org/10.3886/ICPSR00003.v1
Bogue, Donald. Census Tract Data, 1960: Elizabeth Mullen Bogue File. ICPSR02932-v1. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2000. http://doi.org/10.3886/ICPSR02932.v1
United States Department of Commerce. Bureau of the Census. Census Tract-Level Data, 1960. ICPSR07552-v1. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2007-12-13. http://doi.org/10.3886/ICPSR07552.v1
Guo, D. (2008). "Regionalization with Dynamically Constrained Agglomerative Clustering and Partitioning (REDCAP)". International Journal of Geographical Information Science. 22(7), pp. 801-823.