Tagged Questions

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

3k views

How to calculate the maximum distance within a polygon in x-direction (east-west direction) in PostGIS?

I am interested in the maximum width of a polygon, e.g. a lake, in the east-west direction. Bounding boxes will help only in simple polygons but not in complex concave polygons.
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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, ...
3k 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 ...
2k views

ArcGIS - make linear regression across multiple raster layers

I have a series of 5 rasters which represent a value for 5 consecutive years. Is there a way to create a linear regression for each cell over the 5 layers and output the slope? The result would be a ...
194 views

How to estimate the average width of a sidewalk? [duplicate]

I have a table with two polygons representing urban block with and without the sidewalk: geomBlock and geomBlockWithSidewalk. On my city we can approximate the polygons of geomBlockWithSidewalk to a ...
3k 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 ...
1k 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 ...
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When dealing with rasters of varying resolutions should one resample to the highest or lowest resolution?

I'm looking for recommendations on best practices for dealing with raster data layers with different resolutions and projections. The advice I've been given is to always resample to the layer with the ...
3k 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 ...
6k views

Creating noise maps using ArcGIS for Desktop or Open Source Desktop GIS?

In a previous role I helped create Noise Maps for Northern England. The predicted noise levels was done using the IMMI package (which I can recommend) and the cartographic output was done in ArcMap. ...
865 views

Using GIS tools for non-geographical problems

Many other fields have visual/"spatial" problems that can potentially be solved with GIS tools. I know I've used GIS tools for the odd non-geographical task and was wondering how much this happens and ...
14k views

Analyzing differences between two shapefiles to put results into new shapefile?

I have two polygon shapefiles of the same region from two different years (1985 and 1997) and I need to analyse the differences between the two shapefiles resulting in a third polygon shapefile ...
188 views

Dividing polyline layer in clusters with specific requirements in ArcGIS for Desktop?

For my work in ArcGIS 10.2 for Desktop I need to divide line layers into clusters/groups. Currently I am doing this manually, but I like to automate this. The line layers can consist of 50 up to 2500 ...
2k 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 ...
781 views

How can I calculate how many of a certain feature lie within my various buffer rings?

I am using ArcMap and I have a series of real estate parcels mapped along with a series of wind turbines. I have created multiple buffer rings around each real estate parcel with distances (0.5, 1, 1....
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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) ...
2k views

Heatmap algorithm to visualise point diversity

Can anyone suggest an algorithm to generate a heatmap for visualising point diversity? An example application would be for mapping areas of high species diversity. For some species, every single plant ...
3k 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 ...
379 views

What GIS analysis techniques were used in determining Gale Crater as the landing site for the Curiosity Rover?

What specific GIS analysis was used in determining Gale Crater as the landing site for the Curiosity Rover? I'm assuming factors such as slope, elevation, ruggedness, etc were used as well as ...
279 views

Identifying south facing mountain land, above an elevation, within a slope range, less than fixed distance from major roadways

This odd question comes from believing that such an analysis is plausible in a GIS system. Only, I don't how to accomplish the various discrete steps implied from the Title, nor where to get a topo ...
740 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?
341 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 ...
862 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 ...
235 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, ...
4k 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 ...
423 views

SPOT NDVI time series

I have 423 spot.vgt ndvi from first April 1998 till 31 Dec 2009. I want to know how to stack these NDVI to have one image for time series analysis? Or better to ask how is it possible to analyze a ...
195 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 (...
8k views

Reading National Elevation Dataset (ArcGrid/GridFloat/IMG) with python only tools

I've found high precision elevation (1/3 - 1/9 arcsecond resolution) data from the National Elevation Dataset provided by the USGS. It comes int IMG, Arcgrid, and GridFloat formats. I know ArcGrid ...
4k views

Find and list all polygons that overlap with another polygon

I am working with two polygon layers which overlap but are unrelated (one is congressional district boundaries, the other is MPO area boundaries). I would like to generate a list of all the ...
646 views

Finding polygons without right angles using Open Source GIS or ArcGIS for Desktop?

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 ...
2k 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 (...
6k 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 ...
2k views

Summing attributes intersected by under a radius

Apologies - new user. I am working with QGIS on Mac OS X and with shapefiles downloaded from the US Census Bureau that show population data by state and by county. How do I: select certain points (...
892 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, ...
3k views

Where can I download a free dataset containing major ports across the world?

I am working on an analysis and would like to incorporate major maritime ports from across the world. Some initial searching turned up a dataset produced by General Dynamics, however it will be ...
43 views

Distance matrix tool, how to include distances at 0 metres?

I have used the Vector -> Analysis Tools -> Distance matrix to merge two datasets by the closest points. But in my output csv file, the points that match exactly, or that has 0 metres between them ...
2k views

Calculate and add area of overlapping features within polygons

I have a polygon layer of watershed boundaries And a single multipart feature that contains all public lands for the state. I need to find the area of public lands within each watershed and add it ...
497 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 ...
621 views

Mean coordinates in QGIS

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

Our best table-analysis with GIS? [closed]

Sometimes I think about possible analysis using GIS models (I use QGIS 1.8), and I always think about few types of visualization techniques: demographics, traffic flows, distance ones... Thanks to ...
73 views

how to use line feature as stops input in network analyst?

I'm trying to build a certain route with network analyst on a Network Dataset. As an input to create the route I want to use line features. I am trying to do this with network analyst in ArcGIS 10.0 ...