QGIS is a cross-platform GIS application licensed under the GNU General Public License.

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9
votes
1answer
465 views

Calculating spatial correlation between features from two separate layers in QGIS

I am trying to determine whether the presence of large numbers of active duty military troops in an area is spatially correlated with higher/lower levels of violent crime. That is, are the areas ...
9
votes
3answers
13k views

How to give multiple colors to features within a single shapefile?

I want to give multiple colors to different features within a shapefile based on attribute values , is this possible in QGIS ? If yes what is the procedure ? Is there a way to provide color by means ...
9
votes
2answers
338 views

How to make Great Circle Arcs which look good on a Web Mercator map?

I'm trying to create a map, with data indicating some flights, and want to use Great Circle Arcs, to connect the source and destinations. Basically, I want to do something similar to the famous ...
9
votes
1answer
11k views

Draw lines from points in QGIS

(I found here similar questions but they all reffer to ESRI's programs, and I use QGIS) I have a point layer and need to draw a line passing through or in the vicinity of the points (up to 0.5m ...
8
votes
1answer
1k views

Is the use of Google Earth imagery via the OpenLayers Plugin in QGIS legal?

I understand the terms and conditions WRT use of Google Earth imagery in external applications are strict. Years ago ArcBruTile offered such service in ArcGIS the legallity of which was ...
8
votes
4answers
1k views

Can QGIS Read Spatialite Views?

I have a spatialite database I created that spans several years of crime data. To facilitate a real-world scenario where I may simplify the interaction for a user by introducing a View that simply ...
8
votes
5answers
30k views

How to break single polygon into multiple polygons using ArcGIS Desktop or QGIS?

I created voronoi polygons after which I dissolved them on the basis of one attribute. Now there are cases where in for one single attribute "abc" I have3 polygons at different places with same object ...
8
votes
1answer
470 views

Where is this raster offset being introduced in the QGIS processing toolbox?

I'm using the (awesome!) processing toolbox in QGIS 2.0 to reclassify some NoData values in a raster from -9999 to 0, but at some point in the process there's an offset of about 0.2 degrees being ...
8
votes
2answers
1k views

How to split lines into equal segments with QGIS?

I'm attempting to split a curved (wiggle) line into equal length segments. Have used Grass's v.split which works to a degree but does not provide the output I'm after. v.split will extract segmented ...
8
votes
4answers
5k views

How to create different diameter circles round points?

I want to map a tree survey. I am thinking that I will plot positional points of the trees and then add other data like tree type etc. to the attribute table later. Is there a way I can have an ...
8
votes
1answer
472 views

What version of SVG should I be saving my images with for QGIS? Any particular options I should use/avoid?

I have a illustration in Adobe Illustrator that I'm trying to export as an SVG file and add to my map layout using the Print Composer of QGIS 1.7.3. When I add the image, I get strange artifacts that ...
7
votes
2answers
4k views

How to compare two DEMs and show their difference?

I want to compare my DEMs (ASTER GDEM2 and SRTM4.1). I know, that the GDEM has some extreme "holes" with totaly wrong elevations (I found 3 of them in my working area). Now I need to know, if there ...
7
votes
2answers
9k views

How to create a lat/lon grid in QGIS?

I'm using QGIS. How can I create a shapefile consisting of a grid 0.5° latitude and 1° longitude in size?
7
votes
2answers
2k views

How do I use QGIS python console to iterate through simple layer queries and png outputs?

I'm really new to QGIS coding and I'm having a hard time finding (especially) the api classes/functions to carry out actions of the Query Builder window. I'm basically trying to do this: Iterate ...
7
votes
3answers
1k views

How to extract mountain peak points from a given digital elevation model?

For past couple of days, i m trying to determine how many mountain peaks are visible (line of sight) from a given location using POSTGIS. The data i have is DEM for Swiss and address locations from ...
7
votes
3answers
3k views

How to create a user map from CSV?

I dont even know if QGIS is the right program for what I need.. What I need: I need a program with maps(Denmark to be specific), that I could feed with a database of users through a CSV file.. e.g. ...
7
votes
2answers
4k views

How to split an irregular polygon into equal areas?

I am a surveyor and use QGIS for maintaining soil test records on civil projects and am constantly provided with test lot area or number of lots required. These are more often than not irregular in ...
7
votes
2answers
1k views

How to get correct area calculation using Google Mercator?

i use QGIS with openlayers-plugin and i´ve loaded google satellite as a layer. what i want to do is making a shape-layer (polygon) with the goal to get the area values of the polygons. i´ve activated ...
7
votes
1answer
7k views

Import polylines and polygons into QGIS from CSV

I'm assuming this is a simple question, though my efforts have not yet found the answer! I want to import a large number of polylines and/ or polygons into one one or more QGIS layers in order to ...
7
votes
5answers
17k views

How to install Openlayers plugin on Qgis 1.8?

After having installed Qgis 1.8 i am not able to find the Openlayer Plugin. In "the old days" I know I was supposed to check "add 3rd party repositories", but that button has disappeared? I tried ...
7
votes
1answer
5k views

Distinction between Difference and Clip tools in QGIS?

What is the primary distinction between the Difference and Clip geoprocessing tools in QGIS?
7
votes
2answers
12k views

How to draw a Circle with a set radius?

I have a site and want to draw an indicative line in a 5km buffer around the centre of the site. So I want to draw a circle with a radius of 5km. I have a tool for drawing circles and ellipses and ...
7
votes
3answers
9k views

How to add Raster legends in QGIS map composer?

Is there a plugin or method to add legends for raster layers (with a custom colourmap) as an item in the print composer?
7
votes
1answer
5k views

qgis to local postgis connection - fails

It seems pretty clear I cannot connect to a local postgresql installation out of QGIS. This is my first experience with PostGIS. I am using PostgreSQL 9.0 on a win7 machine. I can see the successful ...
7
votes
2answers
3k views

Can QGIS preserve layers when exporting a PDF? [duplicate]

I saw this posted about a year ago (Can QGIS preserve layers when exporting to PDF?) but figured it was worth asking again -- is this possible? My usual workflow with ArcGIS is to export to AI then ...
6
votes
2answers
566 views

How to generate discrete areas from multiple, overlapping features?

I have a point dataset that I want to append some information from a polygon to. My polygon shapefile contains over 500 features. Whilst each of these features represents individual areas they are ...
6
votes
1answer
1k views

How to write vector layer to csv file with geometry by PYTHON?

I use Python try to write vector layer file to csv file with this code QgsVectorFileWriter.writeAsVectorFormat(mylayer, r'c:\temp\xyz.csv', "utf-8", None, "CSV") It can export to xyz.csv but only ...
6
votes
1answer
861 views

How to measure distance between points based on elevation?

I need to be able to measure distances between points, however the distance need to be calculated in relations to elevation. The points are homes of storytellers from the 19th century and the places ...
6
votes
3answers
229 views

mapping over a million points using QGIS

I'm trying to map a CSV with over a million lat/lon points in the US with no metadata. I've never tried to map this much data and want to know what steps I should take. I know it's too much data for ...
6
votes
5answers
6k views

How to load Shapefiles into a remote PostGIS db using command line?

Can we import a Shapefile from a system which doesn't have PostgreSQL installed (client machine) into a system having PostGIS installed? I am getting problem with 'shp2pgsql' and 'psql' since both ...
6
votes
3answers
828 views

Very poor performance of QGIS and PostGIS2. User error or feature? [closed]

I have a large table in Postgis2. It has >500 million polygon, line and point features all happily living in there and the table performs brilliantly in other GIS. I am now trying to just add that ...
6
votes
1answer
525 views

Simulate (Mock) GPS Tracks

I have the following scenario: 1) I need to create GPX files for use in testing of a mobile device. 2) The tracks to be described within will span large distances over long time periods (i.e. it's ...
6
votes
1answer
1k views

Altering composer label items in QGIS with Python

I'm only new to QGIS and Python so this may exists already, and hopefully be easy to do. What I'm hoping to do sometime in the future is build a map book generator using QGIS as the base. In order ...
6
votes
3answers
1k views

How to place multiple symbols on one polygon centroid?

I am using QGIS for visualizing the health conditions of elderly living in an old age home, some of the elderly have multiple medical device with them and I want to show them on the map. Suppose I ...
6
votes
3answers
5k views

What is XYZ format in QGIS?

Basic question, but I have been asked to export data to an XYZ format. Is this the same as CSV files. I am using QGIS 1.8.0. So i am presuming i select the data I want to export, right click its ...
6
votes
2answers
1k views

How to digitize building footprints with orthogonal edges?

Using QGIS, I am trying to digitize an old raster map, and because I ultimately want to load these 2d layers into sketch-up to turn into 3D models, I need everything to be square. Here's a sample of ...
6
votes
1answer
3k views

Is there a way in qgis 2.0 to prevent overlapping labels?

Is there a way in qgis 2.0 to prevent overlapping labels? I have a layer with a large geographical extent, which means a hell of a lot of labels. Many of them collide and it looks really bad. Is ...
6
votes
2answers
914 views

How do you calculate lat/lons from a PostGIS table which has a projected coordinate system?

I have a PostGIS table in a projected coordinate system (EPSG: 28355 or MGA94 Zone55). In QGIS (with the PostGIS manager plugin) I calculate a coordinate by performing the following SQL "UPDATE ...
6
votes
1answer
521 views

Can QGIS map canvas update while python script is running?

I want to automate a periodic refresh of the QGIS map canvas with updated shapefiles. A Python plugin or console script does not allow the map to update until the script terminates. Is there a way to ...
5
votes
1answer
4k views

How to configure QGIS Sextante to use SAGA?

I have been trying to set up SAGA to work using Sextante in QGIS. I have followed the instructions to configure SAGA in Sextante, with the following input in the path for the SAGA folder C:\Program ...
5
votes
1answer
698 views

How does QGIS calculate heatmap values?

I made a heatmap from points (with values) in QGIS, and now try to understand what the values in color scale are. Radius 300 map units (meters) Pixel size 10 map units (meters) Point values are 10-...
5
votes
2answers
2k views

How to add a sequence to the attribute table?

Is there a way to use the field calculator in QGIS to create a range of values in a count sequence with a specified input range? For example, if I wanted to have the values 1 to 5 repeated within my ...
5
votes
2answers
1k views

Correctly merging DEM rasters and eliminating edge effects

I'm using 10m DEM rasters from the NRCS Data Gateway for a large portion of California. The problem is some strange tiling that appears after merging, but isn't present in the original data (before ...
5
votes
1answer
3k views

Is it possible to create and run custom R scripts in QGIS 2.0?

I am new to QGIS and most of the tutorials I have found are for 1.x and the overhaul has me confused. I would like to create R scripts and run them in QGIS. I have read here that it's possible using ...
5
votes
1answer
754 views

Custom Geographic Transformation on QGIS

Is there a way to create a custom geographic transformation with specifics parameters in QGIS like in ArcGIS? Okay, I want to tranform SAD69 system into WGS84. Well, I'm in doubt because in ArcGIS ...
5
votes
1answer
871 views

Why is tiff different in epsg 3857 and epsg 900913 in gdal

When I transform tiff from 4326 to 3857 and from 4326 to 900913 in gdal, I get different result(when display in Qgis) eventhough these two projections(3857 and 900913) should be the same. What is ...
5
votes
2answers
2k views

QGIS relations widget in custom form

I've just begun exploring QGIS relations option, now in version QGIS 2.2, details here: http://blog.vitu.ch/10112013-1201/qgis-relations This is a great implementation of something I've been ...
5
votes
2answers
3k views

Where to store (premade) styles?

I have downloaded a set of premade styles (*.qml). Where do I have to store this files for usage?. I am using QGIS 1.7 for windows. thank you! Updates @Underdark, thanks for answering, if found ...
5
votes
4answers
4k views

How to reclassify a float raster?

I have three rasters which represent distance (in metres) from certain things (bus stops, parks, libraries). I would like to reclassify these rasters so that they get integer values based on the ...
5
votes
1answer
3k views

interpolation methods in qgis

I have a points layer and I want to create an interpolation grid with QGIS 2.0. If I use Raster -> Analysis -> Interpolation the extent of the output raster is good (rectangular shape) but it ...