Ask A Cartographer

Cleaning up a shapefile

February 11 2010 | 0 comments
Categories: Map Data

i have a very large "road" shapefile which was probably derived from a raster.
it contains roads (represented with coupled lines) and trails (represented with single lines). the attribute table is empty so it can't be of any help. i'm attaching a small excerpt as an example.
i'd like to end up with a "roads only" shapefile, which means:

1. delete all the single lines
2. making the double lines "single"

i guess there will be some further cleaning job to do by hand, but can i obtain that with a command on arcmap?

Mapping Center Answer:

The fastest and easiest thing to do is to edit the existing file by simply selecting and deleting the lines you do not want (i.e., the single lines that you think represent trails and the redundant lines along what you think are the main roads.). An alternative is to digitize the main roads from the existing shapefile. Starting with a new feature class (or shapefile), use the Trace tool to trace the lines that you think best represent the location of the centerline of the road, or alternatively select the lines in the existing data and copy them into the new feature class of shapefile.

Because of the lack of attribution, there are few other alternatives available to you -- selecting by location or attributes are not options, and even our generalization tools won't help (e.g., the tool to collapse dual lines to a single line won't work because you have more than two lines for the main roads).

Hopefully, this is the full extent of your data -- if it is, this will be a quick and easy exercise. If it is not and your extent is larger, it will still be an easy exercise, but it will take a bit longer.

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