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So I'm working with some TIGER data for network analysis, and it comes with no speed or time attributes, so I was able to assign average speeds to the various road types, and I was going to use field calculator to populate the time field using the Speed and Shape_Length fields, but all of the lengths are very small, 0.00xxx. Is there something I need to do to convert them, or are they just measured in some strange unit of distance that I am not aware of?

This is what I have:

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The TIGER/Line data use Global Coordinate System North American Datum of 1983 (GCS NAD83). Based on About the 2015 TIGER/Line Shapefiles, each .prj file contains the following:

GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]

Which means the length you get is in (Degree). You need to convert the projection to meter to get the correct length.

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  • Can I use field calculator to do that, or do I need to reproject? I ended up using Meters = Degrees * (meters per degree), where at the latitude in question, a degree is 111010.50m. Does that seem correct?
    – Paul Cory
    Apr 25, 2016 at 16:32
  • It is better to reproject your data to suitable projection (in meter).
    – ahmadhanb
    Apr 26, 2016 at 0:53

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