Sieve mapping
Topic: Remote Sensing, GIS and GNSS · NCERT: Class 12, Ch 4 "Spatial Information Technology"
Meaning
Sieve mapping is the old, manual way of combining maps. Tracings of different maps of the same area are placed on top of one another on a light table, a glass table lit from below. Looking through the stack shows where features overlap, and an output map is drawn from it. Overlay analysis in GIS is the computer form of this method. It is faster, more accurate and can combine many layers at once.
Example
To see how Aligarh, Uttar Pradesh, grew, a planner could trace its urban land-use maps of 1974 and 2001 and place them on a light table. The areas that changed from farmland to built-up land would show urban sprawl.
Don't confuse with
- Overlay analysis: overlay analysis does the same job by computer with digital layers. Sieve mapping uses paper tracings by hand.