Frequent Questions

66 votes

3 answers

94k views

Layers with same coordinate system should align/overlap in ArcMap but do not?

I put 4 different layers into my ArcMap document, but only one of them will show up on the map! I should be seeing the other 3 layers as well. When I do a Zoom to layer, I can see one layer, but I ...

CaliforniaGirl

681

asked Feb 20, 2012 at 2:19

12 votes

1 answer

7k views

Use QGIS expressions to create geometries: difference between geometry generator and geometry by expression

QGIS has a powerful expression machine that can be used (between other things) to create new geometries, based on existing layers. Basically, there are two options: Geometry generator (introduced in ...

Babel

67k

asked Mar 31, 2021 at 8:55

143 votes

5 answers

29k views

Accessing ArcObjects from Python

I would like to be able to script some things that are not exposed via arcgisscripting or ArcPy. How do I access ArcObjects from Python?

matt wilkie

28.1k

asked Jul 22, 2010 at 21:20

83 votes

31 answers

63k views

How to Start Web Mapping?

I want to start working on a web map at work to map some of our statistics by city. I have an idea, but I'm not exactly sure where to start. Are there any definitive resources that provide step ...

Community wiki

Brian L

596 votes

8 answers

556k views

Measuring accuracy of latitude and longitude

I have latitude and longitude as 19.0649070739746 and 73.1308670043945 respectively. In this case, both coordinates are 13 decimal places long, but sometimes I also get coordinates that are 6 decimal ...

Saurabh

6,087

asked Apr 18, 2011 at 7:16

109 votes

16 answers

73k views

Identifying Coordinate System of Shapefile when Unknown?

I have a Shapefile but its coordinate system is Unknown, and there is no *.prj file. How can I identify it now?

com

3,654

asked Mar 28, 2011 at 17:48

11 votes

1 answer

5k views

Changing shapefiles from geographic (WGS84) to projected (EPSG:2263) coordinate system using QGIS

I am trying to calculate service area polygons using the QNEAT3 plug in tool for a project I am doing. However, I got an error before these polygons could be created. 2021-01-04T08:03:38 CRITICAL ...

UnionTpke

193

asked Jan 4, 2021 at 15:58

184 votes

7 answers

230k views

Installing File Geodatabase (*.gdb) support in QGIS

I have spent around 2 days to find the way to open GDB (ESRI Geodatabase) in QGIS (or any other open source software) but still without success. I have downloaded the newest OSGeo4W installer and ...

Miro

9,644

asked May 28, 2012 at 3:57

49 votes

7 answers

48k views

OpenLayers low resolution and/or shifts in QGIS print composer?

I'm having trouble with the OpenLayers Plugin of Qgis and the map composer: If I create an OSM-background layer and if I want to export this, the OSM-Layer looks perfectly all right in the normal ...

desputin

2,261

asked Nov 25, 2012 at 23:51

10 votes

3 answers

7k views

Assigning point IDs to respective start and end attributes of polyline using Arc Hydro with ArcMap

I have two shapefiles, Point and Polyline. I'm trying to populate my polyline layer with the point data ID (systemID) where the lines start to where they end; eg. create two columns (from and to). The ...

JrUser

159

asked Dec 10, 2014 at 4:00

13 votes

1 answer

3k views

Auto incrementing field based on groups within feature class?

I am needing to auto increment a field based on groups within a feature class. I have 8 plots within a given polygon and I need to assign them an ID from 1-8 for each set of plots within each polygon. ...

Becks

133

asked Jun 27, 2016 at 23:10

40 votes

12 answers

72k 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?

Sophie

403

asked May 19, 2011 at 22:32

41 votes

3 answers

15k views

Using QGIS Processing algorithms from PyQGIS standalone scripts (outside of GUI)

I am writing a script which must work outside of QGIS GUI. I call some API functions from qgis.core but I would like to use the processing plugin. I am able to import processing with sys.path.append() ...

vidlb

699

asked Apr 18, 2018 at 9:31

7 votes

1 answer

1k views

Understanding Coordinate Reference System of QGIS Project and Layer

I do not understand why there can be in QGIS different CRS for project and for layers. I have worked previously with subsurface petroleum software and there CRS "stuff" was lot more strict ...

Marin Mirošević

621

asked Mar 29, 2021 at 9:36

263 votes

11 answers

152k views

Difference between projection and datum

What is the difference between a projection and a datum?

fmark

9,371

asked Aug 3, 2010 at 2:25

22 votes

1 answer

6k views

Using customized Coordinate System in ArcGIS Desktop?

I don't know so much about coordinate systems... In my office we use to deal with spatial data coming from archaeological sites. Each site has its own x-y-z coordinate system (GCS). Three simple ...

Maik

461

asked Jan 22, 2014 at 14:49

117 votes

8 answers

326k views

Calculating polygon areas in shapefile using QGIS

How do I calculate areas of an area shapefile in square meters (m²) or in acres (ha)? I didn't find that functionality in the Vector Tools.

desputin

2,261

asked Apr 12, 2012 at 19:05

210 votes

6 answers

548k views

Adding basemaps in QGIS

ArcGIS Desktop has the option of using basemaps from ArcGIS Online. Does QGIS have any such options?

SNT

3,339

asked Feb 12, 2012 at 19:58

53 votes

3 answers

71k views

Reprojecting vector layer in QGIS

I have a series of layers of lines (shapefiles) in My Project. The CRS of some are different and to merge them they all must have same CRS. When I use Processing > Toolbox > Qgis_algorithims >...

razi

531

asked Oct 12, 2012 at 4:57

35 votes

4 answers

26k views

More Efficient Spatial join in Python without QGIS, ArcGIS, PostGIS, etc

I'm attempting to do a spatial join much like the example here: Is there a python option to "join attributes by location"?. However, that approach seems really inefficient / slow. Even ...

jburrfischer

399

asked Jun 23, 2014 at 18:37

29 votes

5 answers

43k views

Enabling CORS in GeoServer (jetty)?

I hope somebody has already figured this one out. I just installed Geoserver 2.9 on a vanilla Ubuntu 16.04 distro. The Geoserver 2.8 method of enabling CORS with the shanbe.hezoun class does no longer ...

Dennis Bauszus

2,279

asked Sep 9, 2016 at 10:16

26 votes

3 answers

15k views

Displaying world country shapefiles centered on Pacific Ocean using Robinson or Miller Cylindrical projection in QGIS?

I wish to display a map in QGIS (world country shapefiles) showing all countries but centered on the Pacific area. I am not familiar with Proj4, so is there any way this can be done in QGIS?

user21658

281

asked Sep 3, 2013 at 9:17

243 votes

4 answers

264k views

EPSG 3857 or 4326 for Web Mapping

The discussion at What is the difference between WGS84 and EPSG4326? shows that 4326 is just the EPSG identifier of WGS84.. Wikipedia entries for Google Maps and OpenStreetMap shows that they both ...

tymtam

2,543

asked Jan 24, 2013 at 7:06

40 votes

10 answers

51k views

Georeferencing vector layer with control points using QGIS?

I have a non-georeferenced vector layer that I need to be georeferenced. With raster layers the task is easy and straightforward, but I have no idea what should I do with my vector layer. I have a few ...

AHaav

501

asked Sep 11, 2012 at 10:24

37 votes

7 answers

46k views

Fixing geometry validity errors in QGIS 2

I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...

Bap

973

asked Sep 3, 2014 at 22:53

59 votes

7 answers

158k views

Calculating Latitude/Longitude X miles from point?

I am wanting to find a latitude and longitude point given a bearing, a distance, and a starting latitude and longitude. This appears to be the opposite of this question (Distance between lat/long ...

Jason Whitehorn

783

asked Feb 4, 2011 at 19:03

42 votes

1 answer

8k 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 ...

the_bonze

807

asked Feb 9, 2012 at 14:25

32 votes

3 answers

30k views

Understanding "Join Attributes by Location" in QGIS

I wonder if there is somewhere an explanation for the parameters that can be set when running the Algorithm "Join Attributes by Location" in QGIS 2.18. I had a look here: Documentation QGIS Testing |...

four-eyes

3,370

asked Nov 11, 2016 at 11:10

27 votes

5 answers

24k views

Finding centrelines from polygons in QGIS

I was wondering if there is a way to create center lines from polygons in QGIS? I have a polygon layer, but ideally need the centerlines as a separate file.

Alan Carr

2,475

asked Sep 20, 2012 at 9:58

11 votes

4 answers

11k views

Determining bare earth DEM from unclassified LAS file?

I have data in LAS format with RGB values created from aerial photogrammetry using a UAV. I am trying to find a solution to extract the bare earth DEM from the point cloud. I have tried SAGA, ...

user32307

111

asked Jun 12, 2014 at 5:18

24 votes

5 answers

26k views

Including variable in where clause of arcpy.Select_analysis()?

I am trying to loop through a shapefile, selecting each feature in turn and copying it to a temporary shapefile to by included in a union analysis. I'm using a cursor to find the ID name for each ...

Flo Harrison

1,062

asked Jun 14, 2012 at 11:45

22 votes

3 answers

20k views

Importing qgis.core when writing standalone PyQGIS script

I am trying to write a standalone Python script in windows 7 that uses qgis.core and various other qgis libraries. I have found an old question on this subject at Writing standalone Python scripts ...

user24956

409

asked Jan 12, 2015 at 16:52

174 votes

8 answers

284k views

Algorithm for offsetting a latitude/longitude by some amount of meters

I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...

Thomas O

2,033

asked Oct 26, 2010 at 22:43

92 votes

10 answers

221k views

Converting projected coordinates to lat/lon using Python

This site returns Point: X: -11705274.6374 Y: 4826473.6922 when you search with the first key value of 000090, as an example. I assume that this is a spatial reference. I am looking for instructions, ...

Vincent

1,031

asked Nov 28, 2013 at 1:42

57 votes

7 answers

160k views

Getting list of coordinates for points in layer using QGIS?

I've got a layer in QGIS that is comprised of points. Its attribute table doesn't have (show) the corresponding x and y coordinates for each point. Is there a way for me to extract a list of ...

hpy

3,147

asked Apr 22, 2011 at 15:07

47 votes

5 answers

92k views

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

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 ...

Bobo

479

asked May 18, 2012 at 8:26

37 votes

2 answers

30k views

Learning ArcPy?

Where can I start to learn ArcPy?

Community wiki

16 revs, 5 users 50%
PolyGeo

32 votes

7 answers

42k views

Joining multiple records to single feature using QGIS

I'm trying to create a join/relate in QGIS where I have a shapefile of buildings and to that I would like to join a non-spatial table (.csv-file) containing people who work in each building. So I have ...

Mick

321

asked Jun 8, 2011 at 21:05

9 votes

2 answers

1k views

Computing dominant area in polygon using ArcGIS Desktop?

First, I have a shapefile consisting of square grids and each grid has an ID. Second, I have a shapefile consisting of different zones (with IDs). A grid ID in the first shapefile can contain many ...

GISnew

359

asked Nov 14, 2016 at 17:29

8 votes

1 answer

4k views

Layer is not valid error in my standalone PyQGIS script/app

I have written a python class which reads properties of map layers from an XML file and creates appropriate memory layers. I have developed and tested this code with QGIS 2.8.2 on a Windows 7 machine (...

Detlev

4,558

asked Jul 24, 2015 at 18:17

110 votes

12 answers

187k views

Installing GDAL with Python on Windows

Can anyone explain how to install GDAL/OGR with Python on Windows? I have Windows Vista and I have tried following the information on the website and it does not seem to bind the *.exe files for me. ...

Community wiki

8 revs, 4 users 48%
GuidoS

77 votes

7 answers

32k views

Creating regular polygon grid in PostGIS

How to create, on the shape of a polygon, a regular grid of polygons/squares of an given size, in PostGIS? I have thought about a function like Creating regular point grid inside polygon in PostGIS ...

mk.archaeo

993

asked Oct 31, 2011 at 19:41

36 votes

7 answers

61k views

Changing CSV layer attribute value from text to number in QGIS?

I read in a CSV file for linking to a .shp file. All the variables that are just numbers came in as text. How do I change the text variables to numeric in QGIS?

HealthMaps

995

asked Jul 16, 2012 at 7:08

141 votes

14 answers

72k views

What are Definition, Algorithms and Practical Solutions for Concave Hull?

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X (Wikipedia)...

Adam Matan

6,790

asked Aug 16, 2010 at 6:05

60 votes

11 answers

68k views

Removing small spaces (slivers) between polygons

I have a set of polygons representing administrative districts. The districts were digitized by hand, and there are small spaces (slivers) between polygons where the polygons should be touching. How ...

zoo

711

asked Jun 14, 2011 at 14:07

46 votes

12 answers

29k views

Map matching links and ideas? [closed]

I'm using OpenStreetMap and its vectorial road network and I'd like to implement a map matcher algorithm. Currently I'm able, for each GPS position, to retrieve the nearest road segment and ...

Community wiki

yonel

39 votes

7 answers

61k views

Performing Raster Reclassification in QGIS

Is there a way to perform a reclassify of a raster image in QGIS? In ArcGIS Desktop you can do that in Spatial analyst Tools→Reclass→Reclassify

Vassilis

3,436

asked Dec 8, 2011 at 13:38

32 votes

12 answers

97k views

Extracting raster values at points using Open Source GIS?

How can I extract values from a raster by points? I prefer not in Arcgis. I prefer in Qgis or Mapwindow or other open source gis.

Vassilis

3,436

asked Nov 16, 2010 at 9:37

4 votes

1 answer

3k views

Graph/Network building and analysis of linked polygons in ArcMap

This is more of a follow-up question to Dividing polygons into *n* number of groups of equal counts with ArcPy? and Grouping village points based on distance and population size using ArcMap, ...

Max K

148

asked Jul 2, 2015 at 14:15

125 votes

7 answers

60k views

Spatial clustering with PostGIS?

I'm looking for spatial clustering algorithm for using it within PostGIS-enabled database for point features. I'm going to write plpgsql function that takes distance between points within the same ...

drnextgis

6,908

asked Jun 28, 2011 at 15:39

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