# Masking out places with elevation below 5 m from a DEM

I have a DEM of a study region; I want to modify the DEM in order to reflect the coastline outlook when the sea level was 5 meters higher than today. What I have done so far is to use 'Raster Calculator' with the quite simple following formula: DEM >= 5. Then, in the returned raster, I have set to 'hollow' the 1 values (representing cells with elevation >= 5m), and to 'blue' the 0 values. How and by which tools can I use the obtained raster as a mask to modify the original DEM. In other words, I want to mask out (i.e., remove) places with elevation below 5 m from the original DEM. I am using arcGIS 10.1 with advanced license.

I am posting my answer in case this could prove useful to anyone jumping here in the future.

In Raster Calculator I used:

``````SetNull("DEM", "DEM", "Value <= 5")
``````

and it did the trick.

• I'm not sure what you're really trying to do here, but this answer creates a 5m cliff at your new sea level (your DEM will have no values between 0 and 5). If you really want to raise sea level by 5m, you'd need to subtract 5 from all cells, then set all values less than zero to zero or null. If you're just trying to create a mask, you can also use Con or Extract by Attribute. Jul 17 '15 at 23:32

SetNull is one way to do this, then follow with IsNull to create a binary polygon and then Raster to Polygon (simplify).

A simpler workflow would be to use Con (SA):

In arcpy:

``````outCon = Con(Raster("elevation") >= 5, 1, 0)
arcpy.RasterToPolygon_conversion(outCon, "c:/output/NewLandSea.shp", "SIMPLIFY")
``````

The Con tool is available interactively using Raster Calculator.

The reason for simplifying the raster to a binary (0/1) representation is for Raster to Polygon: a complex raster either will not convert (floating point is not suitable input) or possibly not finish due to high complexity, by making the raster binary the polygonization is simplified resulting in new land/sea polygons.