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Masking all but lakes on an aerial photo

February 13 2009 | 0 comments
Categories: Map Data

Hello,

I'd like to show just the lakes from an orthophoto (i.e. mask out the rest of the orthophoto.) The lakes are in a polygon layer. Would I use Feature Outline Masks to do this? Is it possible?

Thanks

Mapping Center Answer:

  1. In ArcMap, add your orthophoto raster and your lakes polygons feature class to the layout.
  2. From the Spatial Analyst toolbar, open the Options dialog.
  3. On the General tab, set the Analysis Mask to (Same as Lakes Feature Class).
  4. On the Extent tab, set the Analysis Extent to (Same as Lakes Feature Class).
  5. On the Extent tab, set the Snap Extent to (Same as Orthophoto Raster).
  6. You can also set the cell size on the Cell Size tab by setting the Analysis cell size to (Same as Orthophoto Raster).

    If you have multiple rasters in your layout, this is a good thing to do just to make sure that the lakes raster you are creating will have the same resolution as the original orthophoto. If you only have the one polygon layer and the one raster in your layout, the cell size will default to the same as your orhhtophoto.
  7. In the Spatial Analyst Raster Calculator, double click and click Evaluate.

    This creates a new TEMPORARY raster with exactly the same values as the input raster within the polygons to ther extent of the polygons feature class. Pixels outside the polygons in this new raster will have a value of No Data.

You can also use the Clip tool in ArcToolbox as explained in this Ask a Cartographer question: How do I clip a raster dataset?

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