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

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3
votes
5answers
2k views

Batch processing DEM rasters in QGIS/GDAL

I am attempting to add relief shading to map using .asc raster files, following this tutorial. It works well, but I have only tried it on single tile of raster data which is 20x20km. I want to ...
3
votes
2answers
556 views

Which labelling tool/engine in QGIS will be supported in the long term?

Why does QGIS appear to have two labelling tools? (Note this is not new and old symbology, but that...) there are two different GUIs, one in the toolbar (which gives the Data Defined Settings option) ...
2
votes
2answers
254 views

Project file read error: Unexpected end of file at line 9957 column 1

On reading the answers from a similar question earlier i still cannot retrieve my project. I last used this project in June and obviously something went wrong when saving or creating the new layer ...
2
votes
1answer
348 views

Grass 7 no longer works via the Processing Toolbox on Ubuntu

When I try to execute a Grass 7 algorithm via the Processing Toolbox in QGIS 2.10, 2.8.2 or 2.8.1, I get the following error: Missing dependency. This algorithm cannot be run :-( QGIS ...
2
votes
1answer
93 views

How to define map extents based on a feature's geometry?

There is a polygon geometry in my QGIS project which represents the extents of my map. Does anybody know how to use the data defined override to get the X/Y min and X/Y max coordinates of the polygon ...
2
votes
1answer
308 views

How to define an event for features selected in mapcanvas in qgis using python

I have created a push button, when it is clicked it calls the function 'selectfeatures'. This function will call the Select feature by free hand tool of QGIS and allows the user to select features in ...
2
votes
2answers
540 views

Do I need to remove older versions of QGIS?

I have installed up to 2.6.1 of QGIS on my computer. Is it recommended that i remove all older versions? Will it cause conflict if they remain?
2
votes
1answer
457 views

How to apply a filter to multiple vector layers in QGIS?

I am trying to apply an attribute filter to multiple layers in QGIS at once. The filter is to be applied to .osm data brought in through PostGIS to QGIS. I have tried selecting multiple layers -> ...
2
votes
1answer
918 views

Finding the common borders between polygons in the same shapefile

The question is essentially the same as here, except that I want to do it in qgis. Thus, is there a qgis function equivalent to the ArcMap intersect function that will take a polygon layer and output ...
2
votes
2answers
1k views

Does QGIS attribute edit form support “relationship” data?

Consider I have a geometry table having one-to-many relationship with a no-geometry table. When I create a feature (geometry), I would like to be able to add the relative no-geometry table data in the ...
2
votes
2answers
3k views

How to use the replace string function in Field Calculator?

Within an attribute table I'm trying to replace one string with another using the 'replace' function . As an example, there are a number of features whose field 'NAME' contain the string '(B)' and ...
2
votes
4answers
1k views

How to create random point in according polygon for each dataset entry in a list (with R)

I have an area divided into polygons, and a dataset of observations which has a common field with the polygon layer. I now would like to generate a random point for each dataset entry within the ...
2
votes
1answer
319 views

Split polygon into lines

I have a polygon layer which looks like this . I used the QGIS multiparts to singleparts tool and also polygon to lines. In both cases i got this type of result . I want to extract polygon into ...
2
votes
1answer
2k views

Label callouts in QGIS

Has anyone been using callout labelling with QGIS, either trunk or stable? Used for clustered points. That means the point stays where it is, the label maybe moved if required and a leader (plain or ...
2
votes
1answer
2k views

How can I create a line with three points with Python in QGIS?

I'm new to Python and I'm having some dificulties. I want to create a simple layer with a line in the console of QGIS with Python. How can I do that?
2
votes
1answer
1k views

encoding problem with QGIS 1.8 and CSV import

I have following problem with QGIS 1.8. Lisboa (standalone installer, Win 7 Pro 64bit) - I import CSV - text in CP1250 separated with ";" and using "," as decimal separator. I correctly set the ...
1
vote
2answers
242 views

Open mail client when clicking feature in Attribute Table

One of the attributes/features of my layer contains an email address. I'd like to be able to open the default mail client by clicking on the mail address from the Attribute Table. After some initial ...
1
vote
1answer
232 views

can not delete file after using runalg function

I my plugin I use the runalg function: processing.runalg("qgis:clip",filepath + "/temp2.shp", Layer, filepath + '/' + layerName) vlayer = QgsVectorLayer(filepath + '/' + layerName + '.shp',layerName, ...
1
vote
1answer
1k views

How to add the attributes of selected features to my new layer in pyqgis

I am trying to create a layer from the selected points coordinates. I am drawing a circle to the coordinate of selected points. I also need to add initial attributes of my selected features to my new ...
1
vote
3answers
830 views

How to access user credentials in database connection?

I am trying to automate a couple of things when a QGIS plugin is activated: If Layer A is not in the TOC, add it. This requests username and password to access a PostGIS table using the inbuilt ...
1
vote
1answer
230 views

How to set the path to shapely?

I am using QGIS 1.8.0 on Mac OS 10.8.3 with python 2.7. Thanks to other threads in the forum, I have successfully installed shapely here: ...
1
vote
4answers
3k views

export 3D data dxf file

I'm trying to export a DXF file from Qgis1.8.0 Lisboa and can not have a 3Dfile in Autocad! Or micristation. It results always in 2D file. How can I export height data from a shape file in Qgis? ...
1
vote
1answer
456 views

Find closest point from origin in QGIS and display measure line in composer

I have a location point. there are several constraints areas surrounding the point. Is there a way to calculate the closest point of this constraint from my point and to display the distances as a ...
1
vote
0answers
792 views

Why is my .csvt not recognized? [closed]

I am trying to associate a .csvt file with a .csv file, so QGIS doesn't insist on calling all the fields text strings (thereby preventing the use of graduated symbols). I used the syntax described by ...
1
vote
1answer
9k views

Opening TIFF DEMs in QGIS

I have files, in Tiff format, downloaded from ASTER-GDEM. Can I open this file with QGIS? If yes, how? Thanks in advance
18
votes
0answers
185 views

Output formats for QGIS Heatmap plugin not appearing in drop-drown in Ubuntu

I've been trying to use the heatmap plugin on QGIS (2.8.2) on Ubuntu(14.04) but the drop down for the output formats doesn't get populated. Selecting the drop-down allows me to press OK on the ...
12
votes
4answers
244 views

How to create lines to visualize differences between polygon features in PostGIS?

I've a PostGIS table polygon_b with some polygon features. There is also a table polygon_a which contains the same polygons as polygon_b but with minor changes. Now I want to create lines to visualize ...
12
votes
2answers
596 views

How to clean such a bad shapefile for routing ?

I am trying to clean a shapefile to make it usable for routing with pgrouting, postgis, postgresql. Here an intersection, it seems to be connected but when we zoom …. It is not: Same here : ...
10
votes
1answer
14k views

How to enable “snapping” in Quantum-GIS while drawing polygons?

I tried to draw polygons in qgis-1.7.0 and I somehow can't find or failed to find the "snapping" option. I'm used to ArcGIS-10.0 where you have some snapping options, like placing points of polygons ...
9
votes
2answers
290 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
283 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
1answer
721 views

How to auto-generate map images with different styles in QGIS?

I have got a simple map in QGIS, containing only 1 layer which consists of 10+ features. Now I need to (programmatically) generate about 200 different JPEG map images of the same area. Each map should ...
9
votes
1answer
1k views

How to create a customizabe table in QGIS Print Composer?

I would like to add a custom table to a map layout created in QGIS. I would like a fair bit of control over the look of the table (borders, background colours of the cells, etc.), and it appears that ...
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
1answer
9k 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
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
1answer
451 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
4answers
4k 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
3answers
2k views

calculate area of vegetations in a raster file

How do I calculate area of several vegetation types in a raster (.img file type) image. They are color coded. Am using QGIS (1.8.0) and ERDAS 9.2.
8
votes
5answers
28k 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
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
1answer
468 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
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
1answer
4k 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
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
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
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
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
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 ...