Hot answers tagged catchment-area
You should use the Table > Update Column command to calculate the population. Depending on how your population data is stored (point or polygon), how the dialog is filled out will differ: In the examples: CatchPopn is the attribute in the drivetime catchments table DTCatch that will receive the calculated population count PopnCol is the population count ...
You could perform a watershed analysis yourself, but its a time consuming process. One good source of existing river catchment data is the HydroSHEDS project, which provides high resolution basins for much of the globe, including the UK.
The trick is to Google "UK river catchment map". (Other combinations that include "watershed" don't work.) You will find River basin management plan documents. River basin district maps (downloadable files). An interactive map. Maps by the UK Environment Agency. Scottish river basin maps and data. A search involving "watershed" did turn up a historical ...
If you don't find a map, SAGA GIS has a module called watershed basins that uses a dem and the channel network (your rivers). If you use a coarse dem this goes fast. http://www.saga-gis.org/saga_modules_doc/ta_channels/index.html
I don't think there is a name for this exact technique, but hopefully some of what follows will provide some options: In general, there are many interpolation techniques for moving between a point representation and a continuous surface, such the TIN interpolation method underdark has illustrated. The continuous surface could then be classified by value to ...
This can be calculated quite easily using Voronoi Diagrams (also known as Theissen polygons) based on Euclidean Distance metrics (i.e. "As the crow flies") in GRASS, QGIS, or ArcGIS. In all three of these platforms, the linked tools take as input a point feature class and output a polygon feature class. If you are trying to calculate based on travel time ...
I assume that there is only 1 pixel per polygon that has a maximum value. 1. Find Maximum Value ... use the shapefile to look at the Flow Accumulation Raster and identify the location of the maximum value in each basin. To solve this task (find the maximum pixel value in each polygon) you can use Zonal Statistics (Spatial Analyst). in_zone_data = ...
To make it where you can move a basin and have the polyline follow, you can set up a topology between the point and line layer. The rule most relevant to you is the Endpoint Must Be Covered By rule. This rule enforces that the endpoint of a line must be covered by a point feature in another feature class.
I could see two ways of going about this problem. One is pretty straightforward. The other requires a great deal of supporting data. The straightforward algorithm would rely on convex hulls rather than voronoi polygons. Construct the convex hull of the vector endpoints and vertices for the street segments that fall inside your drive time cutoffs. Then, use ...
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