Spatial Information Technology
Spatial analysis: overlay and buffer
Use buffers to judge access to services.
Spatial analysis is the main strength of GIS. Its tools include overlay, buffer, network analysis and digital terrain models.
Overlay combines several thematic layers of the same area into a new layer, like the old method of sieve mapping with transparent sheets. Example: overlaying the 1974 and 2001 land-use maps of Aligarh revealed how land use changed, and how the city sprawled outwards.
A buffer is a zone of a set distance around a point, line or area. It is used for proximity analysis: what lies near what?
Example: drawing buffers of 2 to 10 km around hospitals in western Uttar Pradesh showed which areas were well served, and which were least served and needed new facilities.
Layers reveal change; rings reveal reach.
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