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How to reduce the size of a contour shapefile?

RickCheney

I am using the latest version of ArcMap for desktop. I have a shapefile which is contour lines. I have two shapefiles for adjacent areas of a map. One of the shapefiles has double the number of contour lines as the other shapefile. I understand that I can display a reduced number of contour lines by using a definition query, but I would like the actual file to contain fewer lines and be more similar to the other shapefile. Any advice on how to do this is greatly appreciated.

The shapefile I want to reduce contains 673,835 lines in the attribute table and is 125 MB

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Cartographic

Topographic

Accepted answers

JoshuaBixby

Since it appears one set of contours is meters and the other feet, you won't get the clean line up of contour lines unless you do some analysis to interpolate a 33 ft contour from 30 and 40 ft contours. For the more dense data set, set up a definition query to select only 30 ft line ( MOD(elev, 30) = 0 ) and then export that layer with the definition query applied as a new dataset.

All comments

AbdullahAnter

If the similar contour lines are identical . you can use Select Layer By Location—Help | ArcGIS Desktop.and make the input layer the double contour lines layer and the selected layer is the fewer contour lines layer . and overlap type (selection method) is ARE_IDENTICAL_TO

ARE_IDENTICAL_TO —The features in the input layer will be selected if they are identical (in geometry) to a selecting feature

AbdullahAnter

You can do this using the tool in Arc toolbox (as the pervious reply) ,Or the tool in selection menu Using Select By Location—Help | ArcGIS Desktop .

RickCheney

Thank you very much for the help. The contour lines represent areas of the map that are on either side on the U.S. Canada border. There is no overlap on the map. Will Select Layer by Location work for this?

AbdullahAnter

Of course not. I have a question.

Do you want to make the two shape files similar in contour values?

AbdullahAnter

there is easy method, just Use Join in ArcGIS map for the layer that you want to reduce.

and make join fields for two layers are elevation field , and check on keep only matched records.

and you will get what you want. so you can export them or something else.

RickCheney

I can try using Join if the data matches well enough, the rows in one attribute table are in the intervals below

1250
1260
1270
1280

and the rows in the other table are in intervals as below

1247
1280
1312
1345

AbdullahAnter

don't try this, I thought it is as:

and other

RickCheney

Thank you Abdullah for all your help.

GerryGarza

Hi,

Since it appears that you are working with two different coordinate systems, I would convert them back to raster DEMs. Then, use the 3D analyst extension to re-contour them exactly with the parameters you need.

RickCheney

Thanks for the help Gerry. I downloaded the data as shapefiles, one from an American source and the other from a Canadian source. I don't have raster or DEM data for this map because the map will be used on GPS only.

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