Run this code in the preamble for a working example of what I'm dealing with.

Census Tract Entity Store

ResourceData[ResourceObject["Census Tract Entity Store"]]; // Quiet
EntityRegister[ResourceData[ResourceObject["Census Tract Entity Store"]]]; // Quiet

Function Declaration

f[x_] := EntityValue[EntityClass["CensusTract", "ADM2" -> x], 
   EntityProperty["CensusTract", "B19013_001E"], "Association"] // 

List of Counties

Click here for Pastebin of list of counties. You have to run this code in order for this example to work.


Take a look at the following line of code. It generates a map of the census tracts in the DMV area, colored by income. When I run it, having run all the code above first, I am seeing that D.C. and Baltimore are blank. See the areas I'm talking about circled in blue in the figure below. (I added the blue circles after the fact)

GeoRegionValuePlot[<|Map[f, dmvCounties]|>, ImageSize -> 500]


My question is: why are D.C. and Blatimore blank? How can I include them in this map as well?


1 Answer 1


If you look at the output of Map[f, dmvCounties], you can see that there are several counties where the value is Null or Missing.

a = <|Map[f, dmvCounties]|>

Sort[a][[-50 ;;]]

enter image description here

I don't see DC in the output but it does look like there's a "Baltimore County" value that is null. Another way to have a look is by just plotting all the keys:

GeoListPlot[Keys@a, PlotStyle -> Blue]

enter image description here

Clearly something missing.

A final check is to simply run f on the entities you are missing:

 f[Entity["AdministrativeDivision", {"BaltimoreCounty", "Maryland", 

enter image description here

while f@Entity["City", {"Washington", "DistrictOfColumbia", "UnitedStates"}] just returns <||>.

Sorry I don't have a solution as to how you can include them, but the why seems that there may be no data in the dataset for those Entities.

  • $\begingroup$ Hmm. I wonder if it has anything to do with the ADM2 specification in my function declaration... Could it be that these metropolitan areas are ADM1 or ADM3? I tried to replace these entity classes, but nothing returned! $\endgroup$ Sep 27, 2020 at 19:21
  • 1
    $\begingroup$ That definitely seems plausible to me. I would guess the issue is related to them being large metropolitan areas, but I really couldn't say beyond that! $\endgroup$
    – Carl Lange
    Sep 27, 2020 at 20:51

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