The process of extracting geographic, statistical, geometric, or scientific information from one or more related collections of GIS features and data.

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4
votes
2answers
773 views

Plugin for average distance from node to polyline in QGIS?

Is there a plugin available that will calculate this? EDIT 1: The red polyline is the average distance of the point to the black polyline. The red polyline is what I want to display. Alternatively, ...
10
votes
1answer
422 views

Spatial operators in R?

How can I do spatial selections or filters in R? I can do this in PostGIS using (e.g.): SELECT * FROM mypoint, mypoly WHERE ST_Within(mypoint.geom, mypoly.geom); and it is similarly a piece of cake ...
7
votes
2answers
742 views

Is there a described GIS method for creating catchment areas based on nearest driving distance?

ie. a combination of Voronoi polygons with isochrones, so that the Voronoi polygons are based on driving distance instead of Euclidean distance. Is there a name or a described method for this?
6
votes
2answers
169 views

What multiplier would you use for calculating estimated population?

Given a number of address points in a given area, what multiplier would you use for calculating estimated population? I have seen 2.5 in a few places, but I was wondering what the generally accepted ...
26
votes
8answers
2k views

When is a 3D Visualisation in GIS Useful?

I can currently only think of two cases: to visualise potential changes in a landscape, such as the effect of adding windfarms, or the addition of a new building to an urban area. However both these ...
12
votes
3answers
289 views

What practices are available for modelling land suitability?

I currently use a "classic" raster based approach of dividing a study area into cells. All input layers are converted to rasters at the same cell resolution and given a suitability rating. A final ...
3
votes
3answers
693 views

Using National Agriculture Statistics Service (NASS) county level crop data to estimate crop acreage in hydrologic regions?

National Agriculture Statistics Service (NASS) provides county level crop (Corn, Soybean, Sorghum, etc) data. I want to calculate crop acres on each subwatershed from the county based data. I'm ...
7
votes
4answers
3k views

How to calculate polygon length and width using open source GIS?

How can I calculate the length and with of polygons using open source tools? By "polygon length" I mean the length of the longest line within the polygon (update: to be correct, I just need the ...
7
votes
3answers
1k views

How to interpret GRASS v.kernel results?

GRASS manual reads: v.kernel - Generates a raster density map from vector points data using a moving 2D isotropic Gaussian kernel ... Ok, but how do I interpret the results? I understand that ...
8
votes
2answers
2k views

How to calculate average slope in a grid?

This is actually a two part question: Which methods are there to calculate average slope by unit (say km²) for a given area? Are there any special requirements on the data - like additional ...
7
votes
3answers
609 views

How to get a list of adjacent lots to a road in ArcMAP and PostGIS/QGIS?

In the following map, I have: A line / road layer A parcel / lot layer The Task: Find and count the list of lots adjacent to the road with their types (parcel_type is a field in the parcel ...
8
votes
3answers
2k views

How to emulate Google Maps driving directions using pgRouting?

Would like to emulate google maps' driving directions functionality but use pgRouting instead. google's data over the project area & scale is quite a bit off so we want to use our own transport ...
8
votes
4answers
2k views

How to represent bimodal attribute value distributions on a map

I'm looking for a visualisation method that enables me to represent bimodal or even multimodal attribute value distributions on line features. A bimodal distribution has two different modes that ...
6
votes
3answers
1k views

Calculating Length of Linestrings in WGS84 in Miles

I have a few thousand LINESTRING features in a MySQL database. I'm trying to figure out the cumulative length of all the lines -- in miles. Using the GLength function I can retrieve the length in ...
19
votes
7answers
6k views

Nearest neighbor between a point layer and a line layer

I've asked this question several times on stackoverflow and irc between #qgis and #postgis and I also tried to code it or implement it my self in postgis with no real answer. Using programming (most ...
5
votes
2answers
474 views

Disaggregating aggregate GIS data using remote sensing

I haven't really done much with remote sensing imagery. I have census data for an area, and a TIFF raster image of the area. I'm sure this is possible, is there a simple way to disaggregate the ...
10
votes
4answers
728 views

Point Pattern Analysis Algorithms

I'm looking for point pattern analysis algorithms and literature on point pattern analysis, online resources and book titles welcome. The topics may range from general descriptions of algorithms to ...