I am trying to use the crosswalks to map 1990 data on 2010 geographies. But, I seem to be encountering an error in the process.
I am only downloading data for the state of Ohio.
I am using the 1990 block group parts to 2010 block groups crosswalk files and I downloaded data for 1990 by block group part. Unfortunately they don’t seem to line up properly.
Joining is occurring in ArcGIS Pro 3.6.0
- The 2010 block group shapefile for Ohio has 9,232 records.
- When I join the Crosswalk table to the 1990 block group parts table there are 8,251 unique 2010 block group records.
- When I join the 1990 block group parts table to the Crosswalk table there are 9,238 unique 2010 block group records.
- In all cases the first record and the last record are the same.
I’m unsure about whether these joins are valid because they don’t result in the same number of block groups as the shapefile.
The web site instructions say to join the Crosswalk table to the block group part table. But, that results in 981 fewer unique records. But, there aren’t any NULL records.
Joining in the opposite direction results in 8 more unique records then the shapefile as well. So, neither join seems to be correct.
Any guidance would be appreciated? Am I missing something?
When joining the crosswalk table to the 1990 block group parts table, it is important to be aware that a single 1990 block group part can be associated with multiple 2010 block groups. One reason you could be seeing fewer 2010 block groups is because your join is only returning the first matching 2010 block group. To fix this, it’s necessary to run a one-to-many merge so that additional rows are added for 1990 block group parts that have multiple observations in the crosswalk.
If you get a data table for 1990 block group parts that’s limited to Ohio, then there will be a few cases of 1990 block groups parts from the Ohio crosswalk that do not match to any in the Ohio data table; these are BGPs from states neighboring Ohio. State-specific crosswalk files include all target zones for the state as well as any source zones that intersect any of those target zones, including some source zones from neighboring states in cases where the Census Bureau adjusted state boundary lines between censuses. In cases like this, to produce a complete set of data for a single state, it’s necessary to obtain source data for both the state of interest and its neighboring states to ensure you have the required input data to allocate to all target zones in the state. These areas can be identified by a GISJOIN code that does not begin with the state code for Ohio (39).
Additionally, there are cases of 1990 block groups parts from the data table that do not match to the crosswalk because they are entirely in coastal or Great Lakes waters; see the note on blank/missing identifiers for reference. These block group parts all have a zero in the arealand column in the data table, and they also have no population or housing units. The discrepancy in the number of 2010 block groups between the shapefile and the crosswalk is for a similar reason as well: NHGIS shapefiles erase all areas that are entirely in coastal or Great Lakes waters, but these areas are still present in the crosswalk.