Week 8 - Raster analysis Flashcards
Advantages of raster analysis
- analyse continuous surface variables, i.e slopes, density, proximity
non-raster surface representations
- contour elevation lines
- triangulated mesh (TIN)
Image raster format encodes __ ____ values
RGB colour
Raster cell criteria
- all cells have to be referenced
- cells have ground resolution
- values are either integer (1,4,7) or floating (1.1, 2.3).
Zonal raster:
- Must be integer values
- value signifies zone ID: (e/g land uses are indicated by a numerical number)
Can raster data represent points, lines and polygons, like vector data?
Yes
Raster Overlay features
- all grid cells has a numerical value (any scale of measurement)
- simpler than vector data overlay
- no sliver problem
- layers must have same cell resolution and coordinate system/projection.
Map algebra
used to execute all spatial analyst tools (e.g two inputs male and female, + together for total pop)
procedure of using algebraic techniques to build models for spatial analysis is called ____
Cartographic modelling
Scale of analysis
- Local: per cell
- Neighbourhood/Focal: local cell neighbourhood (immediate cells surrounding local cell)
- Zonal: defined groups of cell
- Global: entire raster
Local operation
-single raster layer: sin, log
-multiple raster layers: mean, min
Reclassification:
-for different interpretations
- e.g old values range 2-7 to be reclassified to 9
Neighborhood (Focal) operations
- aggregate functions: sum, mean etc
Zonal operations
two inputs:
- Zone (i.e gov. area, catchment)
- Value raster (i.e population, elevation)
Result summary: calculate the selected statistic from the value raster based on each zone in zone raster.
Global distance operations
Types of distances
- euclidean (direct line from cell to cell)
- Incremental (<>^)
- cost distance –> multiple buffers
Operations in Raster Overlays
- arithmetic operators
- boolean operators
- combinatorial operators
- logical operators.
Arithmetic operators
+ - * /
NODATA=NODATA
