QGIS: Becoming a GIS Power User

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:

1. Open the watershed.tif layer.
2. Open the identify tool and check ...