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Fairfax County, Virginia provides a Shapefile here which shows the boundaries of the tax maps as polygons. Each polygon simply consists of four corners, and what I'd like to do is create a table showing the map number and the coordinates of the corners, such as the following:

Map number, bottom-left, bottom-right, top-right, top-left
77-1, -77 32, -76 32, -76 33, -77 33

(though they aren't quite square like this)

I don't have access to ArcGIS software, but do have QGIS and OpenJUMP, and can install any other software that is freely available. I believe this should be very easy but I'm just missing something. Thanks!

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1 Answer

up vote 5 down vote accepted

In QGIS you can use "Extract nodes" to first get the corner points of your polygons. Then, using "Export/Add geometry columns" you can add x and y coordinates to those points. The results will be four lines of data though.

Another way is to copy paste the geometries from QGIS' map window into a text editor. You'll get the WKT representation of the polygons, e.g.

wkt_geom
POLYGON((-0.971664 0.453443,-0.516714 0.827044,-0.245552 0.432353,-1.001793 -0.224462,-0.971664 0.453443))
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Thanks, took me a minute to find those commands (they're under Vector->Geometry Tools). I could then open the attribute table and view the corners and their coordinates. I didn't see a way to dump the table other than copying and pasting. However it will take a little mashing to produce the format I need, since each corner is it's own row, and one corner is duplicated (I suppose it's the beginning and ending node). I suppose I can't expect these tools to give me the data in the exact format I want. Thanks again! –  joshdoe Mar 9 '11 at 1:28
    
The WKT representation should be closer to the format you were looking for. But any solution will require some postprocessing. –  underdark Mar 9 '11 at 7:20
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