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

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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 ...
4
votes
2answers
305 views

How to identify polygon/point shapefiles in python?

I have a script which performs various functions on shapefiles, most of which are polygon-based. However, some shapefiles are point-based and I have to specify where these files are by editing the ...
4
votes
2answers
154 views

Calculating flowpaths downstream of a point

I am assessing the flood risk posed by pipeline failure. I need to calculate the likely flow-paths for flood water downstream of critical locations along the pipeline using GIS. I'm familiar with ...
4
votes
1answer
106 views

QGIS: Plot a layer given with Longitudes [0 360] to [-180 180]

I have a world map in correct Longitudes from -180° to 180°. Additionally, I have a shapefile of data from South America, which shows at 290° instead of -70°. How can I reproject it using QGIS?
4
votes
2answers
1k views

Postgis 2.1 error after update

After a usual update progress - "apt-get upgrade" - I can not connect with qGIS to my PostGIS DB anymore. Error in the qGIS logfile: Your database has no working PostGIS support. Erroneous query: ...
4
votes
2answers
430 views

Create A Maximum-Value Composite QGIS

I am looking to create a Maximum-Value Composite raster in QGIS I have three raster images: Oct 2012 Nov 2012 Dec 2012 All are in TIFF Format, Float32, EPSG:4326 - WGS 84 I want to stack these ...
4
votes
1answer
394 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 ...
4
votes
1answer
553 views

How to extract pixel value counts from a raster in QGIS?

How does one go about obtaining a summary of the counts of cell values within a raster in QGIS? I know QGIS is doing this, in order to provide the summary statistics and histogram in the properties of ...
4
votes
4answers
782 views

Matching GPS tracks

I'm looking for a proper way to process multiple GPS tracks (so time ordered list of lat/lon points) and match/classify that segments, that are covered by multiple tracks: So it's not about ...
4
votes
1answer
1k views

What is the procedure to load LAS files in QGIS 2.0.1?

What is the present procedure to load LAS files in QGIS 2.0.1? After some searching I found a paper outlining the procedure; however, it was for 1.8.something, and related posts here are all rather ...
4
votes
1answer
247 views

How to programmatically detect a canvas refresh or pan/zoom in QGIS

For my python plugin I would like to remove a VertexMarker when the user pans/zooms there map. Which is the best way to detect a canvas refresh or pan/zoom carried out by the user? Can you suggest ...
4
votes
2answers
595 views

How to draw lines from two points in a CSV?

I have a CSV file where one line looks like this: Duration, user, lat-start, long-start, lat-end, long-end 298, Casual,38.9101,-77.0444,38.91554,-77.03818 Each row in the CSV has two points and I ...
4
votes
1answer
457 views

Experiencing transformation anomalies when performing a Save As to convert coordinates between NAD83-Z14 and NAD27-Z13

Good morning all: I have recently discovered QGIS and have been hoping to find a solution for converting bacthes of xy coordinates between two projection systems for our mapping system. I have known ...
4
votes
0answers
1k views

Loading raster from PostGIS DB into QGIS: succeeded yesterday, fails now [closed]

I have a PostgreSQL(v.9.2)/Postgis(v.2.0.3) database which includes raster layers (added through raster2pgsql). To open them in QGIS (v.1.8.0-Lisboa), the "Add Postgis layer" menu will not work; ...
4
votes
1answer
298 views

Personal shell launcher for PyQGIS

I have changed a shell launcher found at http://inasafe.linfiniti.com/html/id/developer-docs/platform_windows.html as to fit my wish: setting the system environment variables to be able to use PyQGIS ...
4
votes
2answers
868 views

Splitting DXF layers into Shapfile layers in QGIS?

When i load a dxf into QGIS all the layers are present in the attribute table. Is it possible to split this "entities" layer in QGIS into its component parts and save each component part as an ...
4
votes
1answer
879 views

How to break (both) lines at their point(s) of intersection in QGIS?

I'm working with a road network where some of the road segments cross each other but no point is inserted at their intersection. Is there a way to break these line to shorter lines at their points of ...
4
votes
4answers
2k views

Where can I download the exercise data for The Free Quantum GIS Training Manual?

Where can I download the exercise data for The Free Quantum GIS Training Manual? The pdf of the manual just mentions the sources of the data, but doesn't give any links.
4
votes
2answers
728 views

How to select the nearest lines to a point layer?

I am a beginner with GIS software and I'm working on QGIS. I have a problem joining the spatial layers. I have a layer with objects in one city and another layer with the streets. I need to attach ...
4
votes
1answer
468 views

How to use scale -rule based renderer in QGIS?

I wish to render a shapefile of builindings such that at scales below 1:5000, they have a border, and above 1:5000, they do not have a border. For this, I went into layer properties, selected ...
4
votes
2answers
733 views

How do I set mmqgis create grid options?

I am having a puzzle about using mmqgis create vector layer option. I want to use UTM CSR this are my options. I want a grid of 20,000 meters in the east and north axis. Nevertheless i have an error ...
4
votes
2answers
758 views

Spatial query of raster data

I have population distribution data as a raster layer and exposure contours as vector (polygon) layers. What I'd like to do is use the vector layer to estimate the population indicated from the raster ...
4
votes
2answers
1k views

QGIS exporting huge SVG [duplicate]

I'm having trouble exporting an SVG(or a PDF for that matter) from the QGIS print composer. I have a relatively simple map that should, when exported as an SVG, be maybe around 1MB in size, tops. But ...
4
votes
2answers
358 views

QGIS Two Raster Data Sets with black line between the two sets where they join?

Where the two Digital Raster Quad sets (topo maps 7.5 Quad) overlap there is a significant thick black line (not a single line but wide and is wider the further south you go on the map). I am looking ...
4
votes
3answers
975 views

How to speed up Postgis raster layer display in QGIS?

i've been importing some digital orthophoto geotif files into postgis 2.0.1 via raster2pgsql tool (i also made 3 levels of an overview table - pyramid). Then i tried to import the layer into qgis via ...
4
votes
2answers
385 views

Is it possible to add a new line in a non-spatial table using Qgis?

While using QGIS, and having loaded a non spatial table (from a dbf or a Spatialite table), is it possible to add a new row to its table attributes? Normally in a spatial layer you have to use "add ...
4
votes
3answers
897 views

How to split features?

I would like to split a shapefile in qgis according to how the polygons overlaps. Don't know how to though? See pic for explanation:
4
votes
2answers
867 views

Looking for an explanation of QGIS Edit Widgets

I have noticed "Edit Widgets" under the Quantum GIS and would like to know in detail the use case and usage of this widget. For any opened vector file, under the Properties -> Fields Tab, for every ...
4
votes
2answers
618 views

How to represent an imaginary flat world in QGIS without using a round-world CRS

Like one or two other users, I'm interested in using QGIS to map an imaginary flat world. A previous answer suggested simply refraining from defining a CRS for such a world, but I cannot seem to make ...
4
votes
2answers
4k views

How can I extract data from OSM which includes the street names?

I am exporting OSM data (in .osm) files to use in qGIS. I am interested in having the street names displayed. I know they are in the OSM data set because they are displayed when I browse the data ...
4
votes
1answer
376 views

Sub-dividing a polygon into smaller polygons

In OpenStreetMap data, some large areas are tagged with a residential=yes tag. Actually within this large polygon there are multiple smaller (rectangular) houses (which are actually not drawn as yet). ...
4
votes
0answers
699 views

Does QGIS have these CAD editing functions? [closed]

I tried QGIS for the fist time today and it seems quite capable for the task that I have in mind. However, I really miss some basic editing functionality from another GIS software that I have to use ...
4
votes
1answer
446 views

Generate centroids for vector polygons based on raster and land-use data using QGIS

Although QGIS has the ability to generate centroids for polygons, I am not sure how to generate centroids based on land-use development using raster data. Here's an example of what I'm trying to do: ...
4
votes
2answers
1k views

How to create an animated map?

I am seeking to create an animated map illustrating the simultaneous movement of different objects across a large area over time. The display should be capable of playing automatically, or by ...
4
votes
3answers
2k views

How to open/display and extract NetCDF files info?

I am working with NetCDF files using R & Matlab and I would like to know if the GIS community is using them. I know that ArcGIS can open & display, however most of the times the results are ...
4
votes
1answer
4k views

Saving Google Earth Location: OpenLayers Plugin in Quantum GIS

I use the OpenLayers plugin to load Google Earth Layers in Quantum GIS to digitize/identify certain features. As my work is large occassionally I have to quit Quantum GIS to resume later. The problem ...
3
votes
1answer
78 views

What causes OTB pansharpening ERROR Inputs do not occupy the same physical space?

When I try to use the OTB pansharpening tool an error comes up and I don not really know what the problem is. I have a RGB and a Band8 map (both from Landsat8) which I want to use for the tool. All ...
3
votes
3answers
164 views

How can I determine which raster attribute covers the highest area of a polygon?

I'm relatively new to GIS and QGIS but I have a problem that I'm not certain how to solve. I searched here for relevant information but found none. (Or, I used incorrect search terms.) My problem ...
3
votes
2answers
220 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 ...
3
votes
1answer
631 views

Is there a QGIS bezier curve tool?

I'm a recent convert to QGIS but have been confused about the lack of support for drawing curved shapefiles, especially when Arc has almost too many. A lot of the work that our consultancy do is based ...
3
votes
3answers
683 views

Convert 800 .hdf4 files to Tiff using GRASS/QGIS/SAGA/GDAL/R

I've have MODIS ndvi data (MODIS_Grid_16 days NDVI) from the iberian peninsula, from February of 2000 to August of 2012 (really big data). How do I batch convert about 800 .hdf MODIS files to .tif ? ...
3
votes
1answer
658 views

QGIS 2.2 problem, loading layer into road graph

I have the road graph plugin installed, but when I try to configure it with the Settings dialogue, no layer names appear in the Layers field. I have tried various shapefiles, but the Settings dialogue ...
3
votes
1answer
253 views

Show alternating contour lines

Is it possible to show only every other counture line? And how do you do that? (Im new to QGIS Lisboa 1.8.0, but even newer to QGIS Dufour 2.0.1, but have used ArcGIS a bit a while ago, and also ...
3
votes
0answers
163 views

Accessing existing instance of qgis from stand-alone python script

For my own data analysis pipeline, I am running a split screen setup with iPython notebooks on one side, generating variables from source data, pushing them to a csv file which qgis then reads/joins ...
3
votes
2answers
967 views

How to resize the map item in QGIS print composer without changing scale?

Is it possible to lock the scale in the QGIS 2.0.1 print composer? Every time I resize the map, the scale is adjusted. This makes trying out different map layouts really annoying.
3
votes
3answers
1k views

QGIS - Convert Vector points to GPS waypoints and route

I'm new here. I have a shape file with a series of points (around 300) using British National Grid. I need to put them on my Garmin Etrex 10 as waypoints. Can someone tell me how to convert this ...
3
votes
2answers
1k views

how to for loop a folder to batch clip rasters by polygon using python and QGIS

I am using python and QGIS 2.0. I am trying to clip rasters in a folder by one polygon feature. It's the first time for me using (let's say) "PyQGIS", I was used to arcpy before. Anyway, I don't get ...
3
votes
1answer
1k views

What expressions for QGIS field-calculator?

I do not understand what language I have to use in field-calculator and labels on QGIS: SQL or Python? And where I can find the possible script/expressions to use? in the image you can see the ...
3
votes
1answer
546 views

Watershed extraction using different DEM tiles

I would like to extract the watersheds for a particular area using QGIS. However, I only have Aster 30m DEMs to work with, each tile covering one degree square. The problem is that I need to use ...
3
votes
2answers
250 views

How to write an equivalent to MapBasic's CreateLine in pyQGIS?

I know this kind of question has been asked, in part, before - specifically: Seeing QGIS Python Commands and: How is object created as line using createline stored in .tab file? but this is a specific ...