ACS Data Users Group

Hi There,

I'm trying to join the demographics from ACS 2015 data with Block Shape files from 2015 on BlockGroupID (Block Group FIPS code) and see some of Block groups are missing from ACS that are in Census Shape file. I'm wondering what is the reason behind this. I'm new to this kind of geographic data and the group itself. Would love to hear some expect options on how I can get complete information.

Attached google drive link contains the Block Groups ID (FIPS Codes) from ACS 2015 that did not match with Census Shape file 2015.

https://drive.google.com/open?id=0B72S8sjziFItS2lJY0JSaUZob0E

Thanks !

Regards,

Mohammed Ayub

Hi Mohammed - have you checked to see if there is any population data for the missing block groups? That would be what I'd look for first - if there is no population in the block group then there would be no reason for there to be a record for that in the ACS data.

-jami

Hi Jami - Thanks for getting back. I realized that I framed my question incorrectly.
Yes, you are right these block groups are not present in ACS 2015 but they are present in Census Shapefile 2015. And my question would be why are they present in Census but not in ACS ? And Census 2010 has some population associated with these block groups, my thinking is
1) Is that because ACS does not capture all block groups but census does
2) or, there are changes over time in the geographical block groups, they are merged or broken out every year depending on lot of factors?

Regards,
Mohammed Ayub

I'm not sure which data tables you are using from ACS 2015, but there is some data suppression for geographies where the margins of error are larger than the estimates. You can see an explanation and list of affected tables here: www.census.gov/.../2016-01.html

Hi Maribeth,
I'm using the data from this site. www.census.gov/.../tiger-data.html
"2011 - 2015 Detailed Tables" -Block group National File -Geodatabase (.gdb file)

So the tables mentioned in the link might not have all the block groups in them ? Good to know. Anyways I combined all the 22 demographic tables/files into one and replaced columns codes with names for our convenience to do analytics.

Thanks !

Regards,
Mohammed Ayub

You are correct that the tables mentioned in the link might have missing block groups, but that doesn't explain your problem.

I think something might be going wrong with your data processing, or else there is a problem with the national block group files. I looked at the South Dakota state geodatabase from the link you provided and I don't see the geographies that you list as missing in the geometry file or the data tables. And looking at the missing Virginia block group numbers, I don't think they exist either (there is no county with code 515).

Virginia's 515 code is the old Bedford City - merged with Bedford County in 2014. There have been a number of tract and block group changes since the 2010 census that are reflected in the most recent ACS data. For example, changes in 2011 are described at: https://www.census.gov/programs-surveys/acs/technical-documentation/table-and-geography-changes/2011/geography-changes.html. There have been changes in Arizona, California, New York, and Virginia. This may explain some of your missing links.

Maribeth Todd yes you are correct they are not in the ACS 2015 file, but present in this shape file:
www.census.gov/.../tiger-line.html - "2015 TIGER/Line Shapefiles"

Dave Stinchcomb Yes I guess that answers my question, now is there a historical database/file that tracks all of these changes every year ? I saw the link you sent but that has it in different HTML pages, hard to track/read in any software.

Thanks to both of you by the way. I'm new to this so learning some new things.

Regards,
Mohammed Ayub