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I have read the "technical" documentation for the TIGER geographic datasets and they fail to describe the way the geometry is encoded. The document claims that the shape files encode the geometry of linear features, like roads, but the documentation shows no explanation of this. For example, the beginning of the spec for the all lines files is as follows:

enter image description here

As you see, it is just a bunch of meta data, not geometry. Not only that, the fields themselves are not explained. For example, MTFCC is described as being a "feature class", but the possible values or feature classes are not described! At the end of the file there is the following:

enter image description here

The last two fields appear to be some kind of key possibly linking to some other file (???) which has nodes in it (???) I have no idea because the spec does not further describe these two fields.

I have two questions:

(A) Where can I find an actual REAL spec that actually describes each field in the TIGER shape files?

(B) Where is the geometry for linear features located? (As in what exact file and field and what is the spec for those fields)?

  • the geometries are stored in the .shp file as in any other shapefile. esri.com/library/whitepapers/pdfs/shapefile.pdf – Ian Turton Apr 5 '17 at 7:47
  • feature class codes - census.gov/geo/reference/mtfcc.html – Ian Turton Apr 5 '17 at 7:48
  • @iant ESRI is not the US Census Bureau, nor in the documentation for TIGER did I anywhere see that the technical documentation for a shape file was not a government document. – Tyler Durden Apr 5 '17 at 12:59
  • but ESRI did write the spec for the shapefile – Ian Turton Apr 5 '17 at 13:32
  • @iant Ok, maybe that is the beginning of an answer. I went to TIGER's web resources and could nowhere find a spec for their data files. If the spec is somewhere else, I want to understand where it is and how it relates to the TIGER files. – Tyler Durden Apr 5 '17 at 16:07
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Your question seems to be from a very new starting point, shapefiles are a de facto spatial file standard that was written many years ago by the 500lb gorilla of the GIS industry ESRI. Many government and commercial agencies distribute their data in this format. It is readable by (almost?) any proprietary and open source GIS so in general people don't bother to explain how the geometry is stored, it just is (and those of us who have read the spec try to pretend we didn't see the bit where the byte order flips half way through).

Now as to what is in a TIGER all lines file the Census Bureau have a reference section on their website, which includes a page on what the MTFCC codes are.

I suspect many of your other questions can be answered by reviewing some of the (many) howtos on the web

  • In my case I am writing software to read the file, so knowing the EXACT specification for the content of the file is crucial. I am not relying on someone else's software. Thank you for the reference to the MTFCC codes. Obviously that information should have been in the TIGER document but was not, thanks for providing it. – Tyler Durden Apr 5 '17 at 16:54
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    Save your self the time and use a library, there are many that have been around for more than 10 years and are fully debugged. – Ian Turton Apr 5 '17 at 17:00

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