Combining data layers - Spatial Data Analysis: An Introduction for GIS Users - page 69

Input layer Intersect layer Output layer

Figure 5.4 Intersect operator.

Input layer Identity layer Output layer

Figure 5.5 Identity operator.

layer features are retained. Attributes from both layers are transferred to the output
layer.
Identity overlays points, lines, or polygons on polygons and keeps all input layer
features (with transfer of attributes for both layers). h e identity overlay is illustrated
in Figure 5.5.
For lines, all input lines are retained but the lines are split and nodes added where
the lines overlap with the identity layer features. For points, all input points are retained
but the ID numbers of the polygon/s within which points fall are assigned to those
points.

5.2.3 'Cookie cutter' operations: erase and clip

'Cookie cutter' operations are widely used—these enable cutting features within a given
feature (termed the 'erase operator') or outside a given feature (sometimes termed the
'clip operator'). Unlike the operators described above, attributes are not transferred
from both input layers to the output layer—instead only the attributes of the input
layer appear in the output layer.