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I need to clip a vector file based on certain values of a raster (Slope > 2%). I can´t find a direct way to do it.

Trying to vectorize the raster first didn´t work.

Is there any tool (ArcGIS or OpenSource GIS) I could use that I haven´t found yet?

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3 Answers 3

up vote 3 down vote accepted

In ArcGIS you can use Reclassify tool from Spatial Analyst to extract values with slope > 2 %.
Reclassify values
Then run Raster to Polygon and finaly clip your vector.

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Marcin, Thanks for your answer. I had tried that before. Unfortunately the converted Vector Slope is too big and ArcGIS always crashes during the last "Clip". I have tried "Repair Geometry" on the Vecto Slope, but still the "Clip" crashes. That´s why I thought it might be a better idea to use the raster for Clipping, if possible. –  Martin Apr 12 '12 at 8:40
    
When converting raster to polygon, select option 'Simplify polygons' - this reduce the number of polygon vertices. Moreover, try to do your analyse in File Geodatabase. –  Marcin Apr 12 '12 at 9:07
    
I have tried those steps already. Unfortunately it´s still not working. Currently I´m trying a work around splitting up the steps a little bit. Let´s see! –  Martin Apr 12 '12 at 9:14
    
What do you mean '"Clip" crashes'? Does it throw any errors or ArcMap is in No response state? –  Marcin Apr 12 '12 at 9:46
    
I always get the following error: ERROR 999999: Error executing function. Invalid Topology [Topoengine error.] Failed to execute (Clip). Looking around on the internet, I think it´s because the resulting dataset is too complex and big. Tried "Repair Geometry", but that didn´t work either :-( –  Martin Apr 12 '12 at 10:22

Marcin, Saurabh, the problem definitely was the size of the datasets. Splitting up the huge dataset, doing the geoprocessing on the different parts and merging them back together afterwards worked without any problems. Maybe datasets with several millions of features are just too much for ArcGIS to handle.

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Can you elaborate your question a little bit? Where is the vector file coming from.

On a side note, do you have access to ArcGIS Spatial Analyst extension, if you do, then you make be able to extract subset of the raster using Raster Calculator. Here specifically you can use the "Con" (conditional evaluation) function.

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Conditional%20evaluation:%20Con

or

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z00000005000000.htm

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My first thought was also CON tool. But in my created Slope rasters this tool didn't recognise VALUE field. That's why I recommended Reclassify tool. BTW the real problem here is not HOW, but operations on huge vector layers. –  Marcin Apr 15 '12 at 19:22

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