# Question about CBSA GIS Files

**URL:** <https://forum.ipums.org/t/question-about-cbsa-gis-files/3846>\
**Category:** NHGIS\
**Created:** [November 12, 2020, 7:35pm UTC](https://forum.ipums.org/t/question-about-cbsa-gis-files/3846 "2020-11-12T19:35:00Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Alan\_Johnson](https://avatars.discourse-cdn.com/v4/letter/a/3e96dc/32.png) [@Alan\_Johnson](https://forum.ipums.org/u/Alan_Johnson)\
**Post date:** [November 12, 2020, 7:35pm UTC](https://forum.ipums.org/t/question-about-cbsa-gis-files/3846/1 "2020-11-12T19:35:00Z")

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I was comparing the 2018 cbsa shapefile I had downloaded from NHGIS to the US Census Bureau CBSA reference map and noticed a number of anomalies, primarily that the NHGIS file includes counties in CBSAs that the Census Bureau does not.

Here is the Census Bureau’s CBSA reference map.

> **[CBSA\_WallMap\_Mar2020.pdf](https://www2.census.gov/geo/maps/metroarea/us_wall/Mar2020/CBSA_WallMap_Mar2020.pdf)**

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**Author:** ![JonathanSchroeder](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.ipums.org/jonathanschroeder/32/70_2.png) [@JonathanSchroeder](https://forum.ipums.org/u/JonathanSchroeder)\
**Post date:** [November 12, 2020, 8:37pm UTC](https://forum.ipums.org/t/question-about-cbsa-gis-files/3846/2 "2020-11-12T20:37:27Z")

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The map you shared is for the March 2020 CBSAs.

NHGIS derives its shapefiles from the Census Bureau’s TIGER/Line files from the same year, so the NHGIS 2018 CBSA shapefile corresponds to the 2018 TIGER/Line files. According to the [2018 TIGER/Line documentation](https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.2018.html), “All legal boundaries and names are as of January 1, 2018.”

The OMB updates the [official CBSA delineations](https://www.census.gov/programs-surveys/metro-micro/about/delineation-files.html) at irregular intervals across time. The delineations that were in use for the 2018 TIGER/Line files (as of January 1, 2018) are the [August 2017 delineations](https://www.census.gov/geographies/reference-maps/2017/geo/cbsa.html).

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**Author:** ![Alan\_Johnson](https://avatars.discourse-cdn.com/v4/letter/a/3e96dc/32.png) [@Alan\_Johnson](https://forum.ipums.org/u/Alan_Johnson)\
**Post date:** [November 12, 2020, 8:52pm UTC](https://forum.ipums.org/t/question-about-cbsa-gis-files/3846/3 "2020-11-12T20:52:48Z")

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Thank you for your reply. I went through some of the reference maps and bulletins and now see that there was a pretty significant change to the CBSA definitions in 2018 which explains the differences.