By going to Raster | Raster Calculator, we can create a new raster layer based on values in one or more rasters that are loaded in the current QGIS project. All available raster bands are presented in a list in the top-left corner of the dialog in the form raster_name@band_number
as shown in the following screenshot.
Continuing from our previous exercise in which we created a slope raster, we can, for example, find areas at elevations above 1,000 meters and with a slope of less than 5 degrees using the following expression (you might have to adjust the values depending on the dataset you are using):
srtm_05_01@1 > 1000 AND slope_05_01@1 < 5
Cells that meet both criteria of high elevation and evenness will be assigned a value of 1 in the resulting raster, while cells that fail to meet a criterion will be set to 0. The only bigger areas with a value of 1 are found in the southern part of the raster layer.
Another typical use case is reclassifying a raster. For example,...