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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0answers
327 views

mean coordinates in qGIS

I am using qGIS v 1.7.4 for MAC and trying to calculate mean coordinates for a set of points using ftools. To calculate my result I am going to Vector -> Analysis tools -> mean coordinates and ...
11
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1answer
506 views

QGis raster terrain analysis - The curvature filter puzzles me

I am a french Master student at university Grenoble INP, and during my master project I have worked on DEM (raster) terrain analysis. Thus, I have read the source code of several QGis-1.7.4 raster ...
8
votes
2answers
393 views

Finding polygons without right angles

Now we are digitizing some buildings in specified area. The obligatory rule for this work - in most cases buildings should have right angles. We are using QGIS with CAD tools for this work. But ...
1
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0answers
119 views

how to set in arcgis network analysis that use every road segment max m times? [closed]

excuse me if my english ins't good. I have one incident and 120 facility. i wanna set criteria in Arcgis network analysis that if any road segment used for example m times, for other route doesn't use ...
1
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1answer
260 views

ArcGis - batch frequency of point groups to single table?

I'm kind of new in the GIS world but have been finding my way around in forums and help places up to now. Still, there's one task I need to perform that I cannot get my head around it or even find ...
2
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1answer
778 views

Hotspot Analysis: Low Values showing as hotspots

Im running hotspot analysis on point data, attempting to examine pollution emissions. I ran spatial autocorrelation first in order to determine the default distance threshold to use in the fixed ...
9
votes
5answers
1k views

Multicriteria Analysis : how to?

I have to do a multi-criteria analysis to answer the question : "which is the best lot to develop". A few of the criterias are : distance of the nearest bus stop (point layer with bus stops) ...
2
votes
1answer
319 views

How to calculate the Zone of Impact using OpenWind

After downloading OpenWind, I am trying to calculate the ZVI for a single Turbine. There is no documention regarding this from the developers. At this point I just want to compare the output of the ...
9
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1answer
248 views

Looking for a trajectory similarity measure

For my final academic work I have developed a compression algorithm for GPS trajectories. I can estimate the quality of the spatio-temporal compression by computing the syncronized euclidean distance ...
3
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2answers
659 views

How can I reproduce Getis-Ord GI* hot-spot analysis tool in QGIS?

I'm trying to find a hot-spot analysis plug-in for QGIS that would perform similarly to the Getis-Ord (Gi*) hot-spot analysis tool used in Arc, but have not been successful. Does anyone have a ...
3
votes
1answer
286 views

How To Determine Frequency Of Overlapping Polygons (Bounding-Boxes)

My starting point is a series of bounding box polygons, representing the extents of all the data sets in my inventory. I am trying to produce an output grid showing the frequency of coverage over the ...
2
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3answers
3k views

Income data on a block level: how does a newbie do it?

I am a complete newbie at GIS data, and am trying to do the following: Figure out census blocks in Miami-Dade (and several other counties) that have average household incomes > $75,000 Get the ...
4
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1answer
413 views

Analysing Information By Vector Grid

I have two vector line datasets and wish to compare the line lengths. While I have already compared the sum of the lengths, I'd like to conduct further analysis down to 250m, possibly lower. I'm ...
2
votes
2answers
164 views

Spatial analysis? Two layers?

One is LandPlot and the other is Soils. When I open the LandPlot attribute table I see I have 500 specific plots of land. When I open the Soils attribute table I see I have 5 types of soils (let's ...
2
votes
1answer
361 views

How to move a Point perpendicular from nearest Line?

I want to move Point perpendicular from nearest line or polygon, and the question is how to do that? example, I have points (house number) near roadbed, and I don't want them to intersect roadbed ...
1
vote
1answer
227 views

Heat Map to find 10 restaurants, 10 retail, and 10 stores open after 6pm within 3 linear blocks

I would like to find where in the City there is a combination of 10 restaurants, 10 retail, and 10 stores open after 6pm within 3 linear blocks. What is the best way to do this? What data would I need ...
3
votes
1answer
187 views

Efficiently classify raster with irregular polygons

I have a project on my desk to classify an elevation model using different elevation breaks for each polygon in the area of interest. In pseudo code: FOR each polygon IN layer: CREATE_MASK FROM ...
7
votes
2answers
449 views

Looking for advice regarding solar potential applications

I have the task of looking into whether it is possible to build a solar potential application which would inform the user whether a roof is suitable for solar panels and a brief report about the ...
7
votes
1answer
193 views

Analysis of GPS error

I'm wondering if there have been any studies which attempt to analyze or characterize GPS error distribution over different situations/conditions (e.g. surrounded by tall buildings/mountains, ...
4
votes
1answer
533 views

Is there an open source tool for both road network analysis and geocoding?

Is there any one open source software package that can perform both road network analysis and geocoding?
8
votes
3answers
592 views

Identification of consecutive points within a specified buffer

I have a point file, hourly relocations of an animal, and I want to be able to place a buffer around each point and calculate the number of subsequent points which are within the buffer zone. I am ...
9
votes
1answer
385 views

Open source GIS tool for mapping health data

Im looking for an open source desktop gis tool that can be used for visualization and exploratory analysis. I want it to be interactive and perhaps display two or more maps at the same time to allow ...
4
votes
1answer
318 views

How to create a service area using both streets and buslines in the same network?

I want to create a network analysis more difficult. Therefore, I want to calculate a Service Area around hospitals next to busstops. But: The network does not only consist of roads and ...
2
votes
1answer
477 views

How to integrate every single street into a network analysis?

This is my first question, but I solved problems before thanks to this great community! It is also my first time working with a network analysis (ArcMap 10) and there are some problems which haven't ...
11
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1answer
182 views

What spatial analysis did the US Supreme Court review in the Perry v. Perez opinion?

The Supreme Court recently issued an opinion on Perry v. Perez which seems like it must have involved evidence based on spatial analysis. The L.A. Times reports: The 9-0 decision set aside a new ...
3
votes
1answer
676 views

ArcGIS tool for indicating changes in land use

I have a couple of shapefiles in which there is some information about land use (polygons) such as water, forests, soils, buildings etc. Each of the shapefiles represents a certain year of the same ...
7
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2answers
606 views

TRI, TPI, or Roughness

I am working on a site selection projection where I will be unable to perform any in situ observations. A key component of the selection process is the ruggedness of the underlying terrain. I plan ...
4
votes
2answers
1k views

How to find the area of raster values within polygon zones?

I'm using ArcGIS 9.3 and I just can't seem to get this right - I've tried tabulate areas, zonal stats, converting to polygons, etc. I'm missing something somewhere. I have a USGS impervious surface ...
4
votes
2answers
299 views

Vector Analysis: Determining area of county land mass without water features

Here are the layers that I have: State / Province polygon file (With Area Field) County / Ward polygon (with no area field), but all the polygons are within the state boundaries Water ways for the ...
5
votes
1answer
341 views

How to find upstream - lateral and downstream zones around urban areas?

I've a DTM and a shapefile of built-up areas. For a fire risk model, I've to find (within a defined buffer zone) two zones around built-up areas: one that is above/higher and lateral and the other ...
6
votes
1answer
981 views

Nearest Neighbor calculation in PostGIS

I'm learning how to use PostGIS and spatial databases for analysis. What I am trying to do is perform a calculation to get the distance for the nearest polygon in a file, using the edge calculation, ...
5
votes
5answers
1k views

Spatial Join on two point featureclasses produces empty output featureclass

I have two point featureclasses that intersect each other. They are in the same projection and dataframe. The issue is, when I perform a Spatial Join the output point featureclass is empty. The file ...
19
votes
2answers
313 views

Ways of expressing geographic questions in machine readable form

A core concept of GIS is answering questions about datasets. From the point of view of a database; SQL with spatial extensions is a way of asking such questions. What other ways can questions be ...
7
votes
3answers
308 views

How to check if parcel is located by golf course

Is there any simple way for me to run millions of parcels through some type of script to see if a shape file parcel is on a golf course? For example if I have a layer that has all the golf courses and ...
12
votes
4answers
16k views

Extract coordinates of polygon vertices in ArcMap 10?

I've got about a dozen polygons in a feature class loaded in ArcMap 10, all in geographic WGS 1984. How do I easily obtain the coordinates associated with each vertex of each polygon in that feature ...
7
votes
4answers
941 views

Spatial query tool for laymen

I know nothing about GIS, but I have what I think is a GIS problem. From spending a few hours googling my problem, I think what I need to do is perform a spatial query, but I'm not sure how to go ...
11
votes
2answers
176 views

How could I rate roads for scenic drives?

relative GIS newbie here. I've been working on a personal project to rate roads on how nice a ride they'd be on a motorcycle. I wrote a Python program to work through road data in the TIGER dataset ...
8
votes
3answers
730 views

Temporal Analysis Tool: Seeking

I am looking for an alternative tool (proprietary or FOSS) that matches the functionality of Temporal Analyst for ArcGIS by DHI Software. The best I could get was the QGIS plugin Time Manager ...
4
votes
1answer
767 views

How can I calculate the vertical distance to the nearest water?

Summary: I would like to create a raster where each cell contains the vertical distance to the nearest water (a decent approximation would be acceptable). The problem is that I'm not sure how to go ...
7
votes
4answers
2k views

GIS Project Workflow?

If you had to teach someone the key stages to a typical GIS Analysis project, what would be the best generic answer? I would like to see diagrams to illustrate this point. Do not think it requires ...
4
votes
2answers
745 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
406 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
700 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
164 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
281 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
653 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 ...
5
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 ...
7
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 kmĀ²) for a given area? Are there any special requirements on the data - like additional ...