Page 49 - Geochemical Anomaly and Mineral Prospectivity Mapping in GIS

Spatial Data Models, Management and Operations 45

Fig. 2-16. Two-map overlay involving a geological map as common first map and different second
maps. (A) Geological map is clipped by map of an area sampled with stream sediments (see Figs.
2-7A and 2-9A). (B) Geological map is overwritten with a map of recently delineated lithologic
units. (C) Geological map is intersected with (or crossed with) a map of stream sediment sample
catchment basins. Further illustration of the intersect operation is shown in Fig. 2-17.

The intersect operation, which is also called the cross or spatial join operation, is
perhaps the most standard of all overlay operations. The intersect operation results in a
collection of all possible intersections between geo-objects in the two input maps (Figs.
1-4 and 2-16C). It is useful, for example, in the process of integrating lithologic
information in catchment basin analysis of stream sediment geochemical anomalies
(Chapter 5). The intersect operation is applicable not only to polygonal geo-objects but
also to linear and point geo-objects. If a map of polygonal geo-objects is intersected with
a map of linear geo-objects, then the output map contains only linear geo-objects. The
output geo-objects in an intersect operation adopt the geometry of geo-objects with the