Terrain Analysis Flashcards
Least Cost Path
Uses Distant Function Analysis to determine LCP from a destination point to a source. The LCP is the path that will “cost the least” depending on which metrics are used to define cost.
Cost surfaces vs. friction cost surfaces
Cost Surfaces-cost distance surface requires a source location dataset and a cost raster as inputs.
Friction cost surfaces-the friction factor (F), to compensate for the bumpiness of the surface, times the distance to travel divided by the miles per gallon the car gets on flat, smooth surfaces
Processing flow for determining a least cost path
To create the path, first a cost distance surface must be created, which requires a source location dataset and a cost raster as inputs.
- The source is the starting point of your proposed feature for analysis.
- A cost raster identifies the cost of traveling through each cell
- Calculates the least accumulative cost distance for each cell from or to the least-cost source over a cost surface.
- Travel direction identifies if the mover is starting at a source and moving to non-source locations, or is starting at non-source locations and moving back to a source.
source, cost raster, cost distance, direction
Flow direction (including data storage)
Creates a raster of flow direction from each cell to its steepest downslope neighbor.
Data storage-
flow accumulation
Creates a raster of accumulated flow into each cell. A weight factor can optionally be applied
Stream delineation
Assigns a numeric order to segments of a raster representing branches of a linear network
-The results of the Flow Accumulation tool can be used to create a raster stream network by applying a threshold value to select cells with a high accumulated flow.
Watershed delineation
Watershed determines the contributing area above a set of cells in a raster.
-The value of each watershed will be taken from the value of the source in the input raster or feature pour point data. When the pour point is a raster dataset, the cell values will be used. When the pour point is a point feature dataset, the values will come from the specified field.
Sinks and Pit-filling
Sinks (and peaks) are often errors due to the resolution of the data or rounding of elevations to the nearest integer value.
-Sinks should be FILLED to ensure proper delineation of basins and streams. If the sinks are not filled, a derived drainage network may be discontinuous.
The relationship between surface flow and aspect
Surface flow is determined by the steepest (slope) downhill direction (aspect).
Slope Calculations- NEAREST NEIGHBOR METHOD
Calculates a nearest neighbor index based on the average distance from each feature to its nearest neighboring feature.
Slope Calculations- 3rd ORDER FINITE DIFFERENCE
Similar to nearest neighbor but corners are considered as well. The first four have a higher weight in the calculation. Good for rough terrain.