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43
votes
4answers
45k views

Where does QGIS write its error log messages?

I want to read and copypaste the error log for the crashes I am experiencing in QGIS 2.0. The error I am getting freezes QGIS so I have to ctrl-alt-del. I can see the last message in the panel, but ...
43
votes
2answers
46k views

How can I convert data in the form of lat, lon, value into a raster file using R?

I have a data set of values over a km grid in the continental U.S. The columns are "latitude", "longitude", and "observation", e.g.: "lat" "lon" "yield" 25.567 -120.347 3.6 25.832 -120....
43
votes
9answers
32k views

Tutorials to handle spatial data in R?

Does anyone know some good tutorials to handle spatial data in R? I know that there are some packages like rgdal and maptools but I haven't actually found usefull tutorials to get in touch with the ...
43
votes
4answers
61k views

Deciding what interpolation method to use for resampling raster data?

Are there hard and fast rules about which interpolation methods are suited to each kind of raster data?
43
votes
4answers
47k views

Joining non-spatial CSV file to spatial data (shapefile) using QGIS?

I have a CSV file which has postcode data in a field, but it is non-spatial e.g. no Easting and Northing. I have a shapefile with postcode in a field and some additional data. I want to join the ...
43
votes
3answers
41k views

Why is law of cosines more preferable than haversine when calculating distance between two latitude-longitude points?

In fact, when Sinnott published the haversine formula, computational precision was limited. Nowadays, JavaScript (and most modern computers & languages) use IEEE 754 64-bit floating-...
43
votes
7answers
18k views

Comparing two spatial point patterns?

If I have two point pattern distributions within the same geographic region, how would I go about visually and quantitatively comparing those two distributions? Also assume I have many points within ...
43
votes
4answers
38k views

Reading KML file into R?

I'm working with huge .kml files (up to 10 Gb) and need an efficient way to read them into R. Until now I've been converting them to shapefiles via QGIS and then back into R with readShapePoly and ...
42
votes
18answers
25k views

Why do you use ArcGIS for Desktop?

I'm new to GIS, having only dabbled with ArcGIS for Desktop for about 4 weeks in 2007. The business I am at wants to target writing complete solutions that involve GIS as it would benefit their ...
42
votes
5answers
21k views

Calculating average width of polygon?

I'm interested in examining the average width of a polygon that represents the road surface. I also have the road centerline as a vector (which is sometimes not exactly in the center). In this example,...
42
votes
12answers
9k views

Representing network flows? [closed]

For a project I'm working on, I need to represent network flows over 1,000 zones with directionality. Any suggestions on displaying the information in a nice and non overwhelming way? Any examples ...
42
votes
5answers
28k views

Fixing non-noded intersection problem using PostGIS

I'm using a PL/R function and PostGIS to generate voronoi polygons around a set of points. The function that I am using is defined here. When I use this function on a particular dataset I get the ...
42
votes
5answers
38k views

How to determine if a tiff is georeferenced or not?

I received a tiff file from someone, but I'm not sure if it's georeferenced. Is there an easy way to check this?
42
votes
7answers
26k views

How to create svg symbols that have modifiable fill color, stroke color and stroke width?

I want to create some svg symbols for Qgis using Inkscape, those symbols must have attributes as described in the question. For the last two days, I have been experimenting as instructed by Sourcepole ...
42
votes
5answers
3k views

Generating equal sized polygons along line with PyQGIS

I would like to create polygons along a line to use them for AtlasCreator in a next step. ArcMap has a tool called Strip Map Index Features. With this tool I can choose the height and width of my ...
42
votes
3answers
49k views

Manually placing labels in QGIS?

Is there a way to manually place labels in QGIS? I have a map which has almost-duplicate labels in some places (e.g. E 1st St and 1st St) and I'd like to remove some of them. Also, I'd like to ...
42
votes
1answer
39k views

Finding center of geometry of object?

Given a set of 2D or 3D points: How to find the center of geometry of an object? According to the following figure, the center of geometry differs from the center of mass if it is calculated in the ...
42
votes
1answer
14k views

Using GeoPackage instead of SpatiaLite, and vice-versa?

I am using now QGIS 2.18, which includes support for GeoPackage format. I know that GeoPackage is like a replacement for Shapefile but not quite so, as GeoPackage has database capabilities. At same ...
41
votes
12answers
35k views

Tablet or smart phone GPS vs “real” GPS

I've been reading a lot today about android and iphone devices being used for spatial data collection in the field and it sure seems to be that single purpose devices such as the extremely popular ...
41
votes
8answers
75k views

How to determine the centroid of polygons?

I have a polygon vector and I want to quickly attain the centroid of this polygon for insertion in a text document. I am working with QGIS. I searched through other questions and although some are ...
41
votes
3answers
26k views

Is it possible to look at the contents of Shapefile using Python without an ArcMap license?

I wondered if it is possible to look at the contents of a shapefile using Python without having and ArcMap license. The situation is that you can create shapefiles from many different applications, ...
41
votes
7answers
263k views

Export Google Maps Route to KML/GPX

Since Google pulled the plug on Google Maps Classic, I'm reluctantly moving to its Google Maps New application. However, I didn't find how to export a route to a GPX or KML file so it can be copied ...
41
votes
5answers
13k views

Curved point-to-point “route maps”

I have recently been looking at airlines web pages that display their routes departing a certain city to all other cities they service. I would like to be able to create similar curved routes between ...
41
votes
5answers
70k views

Splitting shapefile into separate files for each feature using QGIS or SAGA [closed]

I have a polyline shapefile with about 20 kinds of roads. I would like to know how can I create automatically a vector file for each one. I am aware of how to do it using ArcGIS Desktop - see ...
41
votes
2answers
52k views

How do I check which version of GDAL I have and how many?

I have installed in my computer the following software: PosgresSQL 9.3.2.3 PostGIS 2.1.1.1 QGIS 2.0.1 Dufour (this one installed through the OSGeo4w package) QGIS 1.7.0 Wroclaw As far as I know all ...
41
votes
5answers
35k views

Making beautiful maps in R? [closed]

There are quite some nice possibilities to analyse spatial data in R and in the context of my current project I would like to use R more frequently to do that. Until now I plot my maps with ggplot2 ...
41
votes
3answers
17k views

Convert GeoJSON to TopoJSON

How can GeoJSON data to TopoJSON be converted? TopoJSON files are often smaller than GeoJSON and the conversion allows you to incrementally simplify a dataset, if you wish.
41
votes
1answer
18k views

Is WGS84 itself a Coordinate Reference System?

I was wondering the difference between WGS84 and EPSG:4326 (see this). Can then WGS84 on its own be defined as a Coordinate Reference System? Or is it just a datum so that a Coordinate System must ...
41
votes
1answer
7k views

Coordinate system for accurately calculating areas of polygons that cross UTM Zones?

I have multiple polygons, all located offshore around the UK. I am trying to calculate the areas of these polygons in square kilometres, without splitting them by UTM zone. Is it possible to do this ...
40
votes
6answers
22k views

Migrating geodatabase data into PostGIS without Esri apps?

Can you tell me how I can load geodatabase data into PostGIS without having to install Esri apps? The solution I found online talked about using ArcGIS to convert GDB to SHP and then importing SHP ...
40
votes
1answer
23k views

Defining new custom projections in QGIS?

I'm trying to define a projection in QGIS. I want to add North America Albers Equal Area Conic. From the spatialreference site I copied the proj4 line: +proj=aea +lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-...
39
votes
15answers
7k views

Using Computer Games to display GIS data?

Besides being a GIS user I'm a big computer game fan. Games like Civilization, Minecraft, World at War and many others have a very powerful engine to display huge maps in a beautiful way. Is it ...
39
votes
6answers
22k views

Shapefile PRJ to PostGIS SRID lookup table?

I was wondering if there is such a thing as an shapefile PRJ to PostGIS SRID lookup table? Something that can translate the most standard shapefile PRJ definitions into the likely SRID. When using ...
39
votes
5answers
23k views

Change style properties of several layers simultaneously?

I'm working on bulk data. I have a few hundred GeoTIFF images imported into a QGIS project, and I'd like to modify their layer properties - things like the no-data-value, transparency of certain pixel ...
39
votes
11answers
41k views

Is there a way of auto_increment for the ID column in QGIS

I'm creating a fictive map and so I need to create lots of points, lines and for sure polygons. Later on I export my data as geojson. But before that I aways have to go and give every element an ...
39
votes
4answers
9k views

Using directional shading on boundaries for cartographic effect in ArcGIS Desktop?

The attached screenshot of a National Geographic map shows some beautiful directional shading of boundaries. I'm trying to reproduce this sort of shading for a burn perimeter map, as I want to ...
39
votes
4answers
62k views

Loading OpenStreetMap data in QGIS?

In QGIS 1.8 I used the openstreetmap plugin to request data from the server, or open a .osm XML file, which produced 3 layers (polygons, polylines and points) in QGIS. This was great (give or take ...
39
votes
4answers
39k views

How to insert a GeoJSON polygon into a PostGIS table?

I need to insert a polygon from GeoJSON to my PostGIS table. This is how the SQL query looks like. INSERT INTO tablename (name, polygon) VALUES ( 'Name', ST_GeomFromGeoJSON( '{ ...
39
votes
12answers
52k views

Where to get 2010 Census Block data?

I would like to download 2010 Census Block Data for several towns and I can't seem to find it on American Factfinder. Is it there? And if not, does anyone know where I could find it?
39
votes
3answers
36k views

How to run a simple python script for QGIS from outside (e.g. Sublime Text)?

I would like to run a few small and simple python scripts for QGIS (Mac) from "outside" of QGIS. With outside I mean in this context, either the normal os command line (terminal.app) or even better, ...
39
votes
6answers
32k views

Visualizing large datasets with Leaflet

When using Leaflet to visualize a large dataset (GeoJSON with 10,000 point features), not surprisingly the browser crashes or hangs. A sub-sample of 1000 features from the same dataset works ...
39
votes
4answers
12k views

How to migrate from ArcGIS for Desktop to QGIS? [closed]

Our lab has about 10 projects in ArcGIS 9 (a couple are made in ArcGIS 10) that includes the following in each: A georeferenced (WGS1984 geographical projection) raster seafloor image, representing ...
39
votes
6answers
52k views

Trilateration using 3 latitude/longitude points, and 3 distances?

I want to find out an unknown target location (latitude and longitude co-ordinates). There are 3 known points (latitude and longitude co-ordinate pairs) and for each point a distance in kilometers to ...
38
votes
15answers
109k views

Converting MapInfo TAB and/or MIF to SHP using free tools or ArcGIS for Desktop core product?

How do I convert MapInfo TAB and/or MIF files to SHP using only free tools or ArcGIS itself? I've not had much luck trying to do this in the past and I don't want to have to shell out for the ArcGIS ...
38
votes
12answers
67k views

Exporting feature class into multiple feature classes based on field values using ArcGIS Desktop?

I have a feature class with over 2,000 features, and I need to make them all individual feature classes based on a field. Is there a way to do this?
38
votes
9answers
9k views

Machine Learning Algorithms for Land Cover Classification

I am interested in learning what software exists for land classification using machine learning algorithms (e.g. k-NN, Random Forest, decision trees, etc.) I am aware of the randomForest package in R ...
38
votes
9answers
84k views

Generating random locations nearby?

I am trying to create random locations nearby my location. What i want is to create random latitude/longitude pairs inside a 200 meters circle surrounding my location. This is the formula i came up ...
38
votes
10answers
33k views

Open Source Tool capable of reading Esri File Geodatabase (.gdb)?

I have an ESRI File Geodatabase (.gdb) file that I would like to convert to shapefile (or any other non-proprietary format). Are there any Open Source tools to do so?
38
votes
3answers
38k views

Ignoring invalid input features with Intersection tool in QGIS?

In QGIS 2.18, when I used the Vector > Geoprocessing Tools > Intersection tool, I was able to check an option which said "Ignore NULL geometries [optional]". Now I've downloaded QGIS 3.2 and that ...
38
votes
1answer
32k views

How to convert/typecast from Polygon to Multipolygon in PostGIS?

Is there any way to typecast Polygons to Multipolygon type? For example, I have created a circle using ST_Buffer() on a point. The return type of that function is of Polygon type. The problem is that ...

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