Projection for interior points in tabular data

NHGIS
1

Hello,

I noticed that tabular data (eg for 1990 and 2000 census blocks) contains coordinate columns for interior points of the polygons. I am wondering what projection is being used here. I have read elsewhere (https://www.nhgis.org/gis-files) that NHGIS generally uses “Esri’s USA Contiguous Albers Equal Area Conic Projected Coordinate System” implying EPSG codes of 5070 or 102003 but neither of these seem to fit. I would really like to use the points directly in the tabular data since it would save me a lot of other geoprocessing, but this requires knowing what the projection is. And better documentation of this point would probably help other users too.

Thanks,
Ben

2

Dear Ben,

The interior points in the tabular data are in latitude/longitude (NAD83). Those coordinates come directly from the Census Bureau’s published data files, and we recently started making them available via NHGIS. The codebook that comes along with the data file indicates that they are latitude and longitude:

    INTPTLAT:    Internal Point (Latitude)
    INTPTLON:    Internal Point (Longitude)

We do not include the datum for those points in our documentation though.

Sincerely,
Dave Van Riper
IPUMS