[GIS] How to calculate raster area or number of cells for multiple classes in a raster

qgisraster

I have a raster with many classes and I want to know the area or the number of cells for each class.
I found quite a few posts on this topic (see links below). None of the suggestions matched my wishes. I do not want to convert to vector since my raster is fairly big. I am looking for a tool similar to the summarize functions available for vector data, with a table as output.

The raster is a 32bit float tif with 5 unique values (1.0, 2.0, 3.0, 4.0 and 5.0) as classes as a result of classification with QGIS SAGA-Toolbox.

QGIS solutions are preferred. Related posts:

Calculating raster area?

Calculating area of vegetation in raster file?

Calculating area of rasters in QGIS?

Best Answer

You can use GRASS GIS r.stats as a plugin in QGIS or in stand alone GRASS:

r.stats calculates the area present in each of the categories of user-selected raster map layer(s). Area statistics are given in units of square meters and/or cell Counts

If you need more options like different units use r.report:

r.report allows the user to set up a series of report parameters to be applied to a raster map layer, and creates a report.

Related Solutions

[GIS] How to calculate total number of data cells in raster

couple of options that occur to me without getting too deep in your code. Both rely on a zone mask, which you could make by pushing your raster, which is presumably a mix of values, through a Con (doc here) so output has only values of 1 where there is data. Can take that mask/zone grid and use it w/:

zonalgeometry (doc here)
@whuber's suggestion of zonalsum the 1s and multiply by the area.

Alternatively, you could use a cursor to sniff the one and only VAT row and extract the COUNT field (not sure of the syntax for this back in 9.3). Example:

---EDIT---

csr = arcpy.SearchCursor(gridVAT)
row = csr.next()
min = row.getValue('COUNT')

Thinking COLUMNCOUNT + ROWCOUNT won't work on irregularly shaped (i.e., not square and oriented w/coord sys).

Agree w/@radouxju, don't really see the purpose of the ASCII representation. Seems wildly expensive, but can't see your whole workflow.

[GIS] How to Create a Catchment Area of a Polygon (Wetland) using DEM in QGIS or Whitebox GAT

If you have a vector polygon representing a wetland, then in Whitebox GAT, you just need to convert that polygon to a raster using the Vector Polygons to Raster tool. Use the DEM as the 'Base Raster File' to ensure that output polygon raster has the same dimensions as the DEM. Then you simply need to input this image as the 'Input Pour Point' file to the Watershed tool. So long as each wetland polygon is assigned a unique ID, each associated watershed will be delineated in the output watershed raster.

Best Answer

Related Solutions

[GIS] How to calculate total number of data cells in raster

[GIS] How to Create a Catchment Area of a Polygon (Wetland) using DEM in QGIS or Whitebox GAT

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