GIS 205: Raster Analysis

Raster data examples

Spread of a disease

Animal migrations

Crop yields

Hazard analysis of urban sites

Forest growth analysis

Local Operations

Operates on one cell location

Any math operation that can be performed on numbers

Neighboring cells not taken into consideration

Moving Window

Operates on a geometric neighborhoood

Uses a moving window

Are of different shapes and sizes

Moves left to right and down (with overlap)

High and Low Pass Filters

Can be used with a mean kernel to reduce the difference between a cell and surrounding cells

Known as low pass or high pass filters

High pass filters

Return small values when smoothly changing values

Large positive values when centered on a spike

Large negative values when centered on a pit

Clip

Helps to only retain certain cells

Zonal Functions

Zones are collections of pixels that share a common integer value

Zonal statistics

Calculate statistics for those pixels that fall within each zone

Can be output as either a new raster image or a table

Global Operations

Operates on the entire grid

Requires the consideration of all pixels in a grid, though they may not use all pixels

Cost Surface

Minimum cost of reaching cells in a layer from one or more source cell

Units can be money, time, etc

Distance measured with a fixed cost per unit to calculate travel cost

If multiple source cells, lowest cost is typically placed in the output cell

Friction Surface

cost=cell difference*friction

One-to-Many Relationships

Links one feature (like a parcel) to multiple records in a table