shapefile - Calculating polygon area inside another polygon in QGIS

Is it possible to calculate the area of colorful polygons (yellow, yellowish/reddish and red) inside another shapefile (purple outline, also polygons) in QGIS.

For example the polygon that is marked with red line: i'd like to know how much there is yellow, red etc inside the polygon with purple colored outline (area).

Answer

You can do it using the following steps:

1. Select the target polygon (purple color)


2. Use intersect tool from Vector -> Geoprocessing tools -> Intersect


3. In the Input vector, choose the colorful polygon layer, and choose the purple layer in the intersect layer field


4. Check Use only selected, as you can see below:

5. Save the output intersected layer


6. 
   

   Start editing of the output layer and add new field in the attribute table, and give it a name Area, and in the expression, write $Area, and press on Update All to update Area field. Save edits.

   
   

   Make sure that both layers have the same projection.