Handling null values
Null values are a particular type of values that are used to indicate cells where the value for a given layer is not defined. Understanding how to use them is important to avoid wrong results when performing analyses but also to use them as a tool to get better and more correct results. This recipe explains some of the fundamental ideas about null values in raster layers.
How to do it…
The watershed.tif layer contains the area of a watershed. Cells inside the watershed are cells from which water will eventually flow into the outlet point of the watershed. The remaining cells belong to a different watershed. To mask the DEM with the watershed mask, follow these steps:
Open the
watershed.tiflayer.Open the identify tool and check whether the cells that belong to the watershed have a value of 1, and the ones outside, have a value of
no data.Try clicking inside and outside the watershed; in your Identify Results dialog, you will see the results, as shown in the following screenshot...
