DEM to Polygon

PawanThapa

Dear Experts,

Working on a DEM (30m x 30m raster) of a large area, I need to find out the area (polygons) which is greater that 5,000 hectares and within which average slope is less than 10 degree. The shape of the area/polygon- more it is towards square or reactangle better it is.

I cannot figure out which step would enable me to achieve this. Can you experts guide me or give me hint, please?

curtvprice

The raster tools have capabilities that make this pretty straightforward. Check out the following tools:

• Slope
• Con
• Region Group
• Zonal Geometry

I suggest trying them on your data (using a smaller environment extent to save time) until you get a workflow that gets you what you want. Laster, you can expand the extent to process the full study area.

You can use the magic of map algebra to do this analysis in Raster Calculator, using an expression that combines these tools. This may be helpful if you want to easily tweak your parameters once you have the process working. In this example I am assuming your xy coordinates are in meters so 1e6 is a 1 km2 (1000x1000 m2) minimum area.

RegionGroup<SPAN class="punctuation token">(</SPAN>Con<SPAN class="punctuation token">(</SPAN>ZonalGeometry<SPAN class="punctuation token">(</SPAN>
    RegionGroup<SPAN class="punctuation token">(</SPAN>Con<SPAN class="punctuation token">(</SPAN>Slope<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"dem"</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="operator token"><</SPAN> <SPAN class="number token">10</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="number token">1</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">,</SPAN>
        <SPAN class="string token">"Value"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"AREA"</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="operator token">></SPAN> <SPAN class="number token">1e6</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="number token">1</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

Once you have these zones defined, you can convert them to polygons with the Raster To Polygon tool. A good way to then identify the "rounder" polygons would be to calculate the area / perimeter ratio (larger ratios are "rounder" polygons).