Tabulate Area for large datasets

Question

I have been struggling trying to use Tabulate Area in Arc 9.3 for a large raster dataset.

I have one raster with 8 land uses and another vector layer with zones (which I converted to a raster with the same resolution as the raster with 8 land uses, I also used the snap raster function when I did this).

When I use tabulate area separately for the two datasets, I get different areas. To cross check, I tabulated area using one of the polygons in the vector dataset for tabulate area, and got quite a significant difference in area as well.

Any suggestions on what would be the best way to tabulate area for a large dataset?

Answer 1

You need to be very careful using tabulate area. The tool is helpful, but has some "gotchas".

• Watch out for sending in overlapping zones. Zones cannot be overlapping as the vector is rasterized and two zones cannot be represented in the same cell. Its a bummer Esri doesn't handle this out-of-the-box.
• Setting snap raster is great, but you should also set the output extent environment variable.
• If all else fails, manually convert your zones to a raster and run Tabulate Area using the raster as your zones. This will may give you more consistent results. The documentation states:

It is recommended that you only use rasters as the zone and class inputs, as it offers you greater control over the vector-to-raster conversion. This will help ensure that you consistently get the expected results.

In general, you really need to closely read the tool's documentation. I've gotten burned pretty bad on Tabulate Area and Zonal Statistics so beware...

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=tabulate_area