Forwarding a question from one of our state agencies.  I will forward any replies and appreciate any help you can provide.

John

John M. Anderson

Map Librarian and Director

Cartographic Information Center

Department of Geography & Anthropology

LSU

Baton Rouge, LA 70803

(225) 578-6247

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     Working with the Broadband data, I have encountered an issue for which I have no clear resolution.  The data they gave me include:

1. 2020 US Census Blocks

2. FCC Auction 903 Data in Census Block Groups

3. FCC Auction 904 Data in Census Block Groups

In dataset 1, I have Census Block IDs with 15 digits.  In #2 and #3, the data are in Block Groups identified with a 12-digit code

     I need to perform a Join to link the Block Group data with the Census Blocks.  I assume a Census Block has a one-to-one relationship to a single Block Group [they “nest” into the Block Group].  My Census Blocks dataset does not include a “Block Group Field” for me to execute the Join.  I made the assumption that the first 12 digits of the Census Block ID would allow me to ID the Block Grope.  So far, it does not seem to be the case.  When I go to the map and select a  Block, the first 12 digits don’t match the Block Group [from dataset #2 or #3] that corresponds to that location.  Does that make sense?

     Since the first 11 digits match, I am thinking that I may be working with 2020 Blocks and 2010 Block Groups.  It is also not clear that the geometry all line up.  Since Block Groups are larger than Blocks, ever Block Group Boundary sol fall on a Block boundary.

     Any clarification on the relationship between Black IDs and Block Group IDs would be very helpful.  Here is an example of what I am seeing:

        Block           221210204023001

Block Group     221210204021

These are comprised of:

        22 = State

        121 = Parish

        020402 = Tract

It is not clear to me how I match this Tract ID with its corresponding Block Group ID [3001 v. 1]. 

     In an effort to Join the two tables, by “Block Group” [whiz is not a field in the Block data], I need to construct a new “Block Grope” field, based on the Block ID.  rom this, the only thing I can figure is:

Block Group

Block   221210204023001  >      221210204021  [22121020402xxx1]

Will this correctly map Blocks to Block Groups?  The only other conclusion I can make is that my Blocks and Block Groups come from the 2020 and 2010 Census, respectively.