All Questions
155,059
questions
584
votes
8
answers
517k
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 ...
- 5,967
263
votes
11
answers
149k
views
Difference between projection and datum
What is the difference between a projection and a datum?
- 9,371
231
votes
4
answers
240k
views
EPSG 3857 or 4326 for GoogleMaps, OpenStreetMap and Leaflet
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 ...
- 2,423
207
votes
6
answers
514k
views
Adding basemaps in QGIS
ArcGIS Desktop has the option of using basemaps from ArcGIS Online.
Does QGIS have any such options?
- 3,299
184
votes
47
answers
119k
views
Seeking examples of beautiful maps? [closed]
Oftentimes when we make maps it is based on our subjective interpretation of what is aesthetically pleasing. I would like it if people posted examples of beautiful maps, displaying any phenomena in ...
182
votes
7
answers
221k
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 ...
- 9,376
177
votes
5
answers
200k
views
Difference between WGS84 and EPSG:4326
What is the difference between WGS84 and EPSG 4326?
It seems like for a given dataset it might be both WGS84 and EPSG:4326.
- 2,126
152
votes
8
answers
244k
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 ...
- 1,813
143
votes
5
answers
28k
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?
- 27.9k
142
votes
42
answers
20k
views
What free programs should every GIS user have installed?
Note: This question is specifically about installed, desktop software. There is another question specifically about free cloud-based software and services.
What free programs should every GIS user ...
140
votes
14
answers
67k
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)...
- 6,700
138
votes
17
answers
88k
views
Comparing various JavaScript mapping libraries?
I am working on a web-based mapping system and I'm trying to figure out which library to use.
These are links to comparisons of available libraries:
Laurent Jegou's benchmark (from 2010) is a global ...
124
votes
7
answers
58k
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 ...
- 6,828
118
votes
13
answers
8k
views
Accounting for Colour Blindness when designing maps?
Depending on what you read, 7 to 15% of the general population has some form of colour blindness.
Can this be accounted for in map designs and, if so, how?
- 27.9k
117
votes
8
answers
93k
views
Choosing OpenLayers or Leaflet? [closed]
I was debating with one of my collegues on OpenLayers v/s Leaflet. I made a point that OpenLayers is much better API if we wish to build a project, where you need direct connectivity to the Geoserver ...
- 4,335
117
votes
4
answers
491k
views
Does Y mean latitude and X mean longitude in every GIS software?
I am using Mapinfo and it has Y as latitude and X as longitude. Is that the same case for all mapping software? As for any country their respective value is multiple of 1 or -1. So for Nepal can I say ...
- 4,276
114
votes
7
answers
177k
views
Differences between DEM, DSM and DTM?
I am listing some of the acronyms used in our work and had to stop to think about whether to list these together or separately:
DEM: Digital Elevation Model
DSM: Digital Surface Model
DTM: Digital ...
- 35.6k
113
votes
23
answers
138k
views
Converting between KML and shapefile (SHP) format
My users are sending me point data that were digitized using Google Earth.
How can I convert their KML to a shapefile and vice versa?
- 1,353
113
votes
14
answers
290k
views
What ratio scales do Google Maps zoom levels correspond to?
Can anyone provide me with a link (or some details) on the actual ratio to "zoom level" figures for Google Maps?
e.g. Google Maps Level 13 = 1:20000
- 1,281
112
votes
8
answers
292k
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.
- 2,211
111
votes
5
answers
261k
views
Merging multiple vector layers to one layer using QGIS
I've imported several shapefiles which where exported from a Mapinfo .tab. Several .tab-files are imported resulting in 20+ layers.
Afterwards I want to export it to GeoJSON; but I'm reluctant to ...
- 2,239
109
votes
12
answers
180k
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.
...
106
votes
16
answers
69k
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?
- 3,626
105
votes
4
answers
37k
views
What are the pros and cons of PostGIS geography and geometry types?
My company uses geometry (the_geom) data type for storing geospatial data.
I've recently been acquainted to the concept of geography (the_geog) data type which, as I understand it, stores the SRID ...
- 6,700
102
votes
11
answers
58k
views
Self-hosting Mapbox vector tiles
As presented in a talk at FOSS4G Mapbox Studio allows to create Mapbox vector tiles and export them as a .mbtiles file.
The mapbox-gl.js library can be used to dynamically style and render Mapbox ...
- 1,811
96
votes
27
answers
138k
views
Python GDAL package missing header file when installing via pip
I asked this question on Stack Overflow before I realised this site existed. As this site it more appropriate, I'll ask it here too.
I'm trying to install gdal from pip pip install gdal inside a ...
- 1,061
94
votes
5
answers
121k
views
Renaming attributes/fields in shapefile attribute table using QGIS
I would like to rename some fields in my attribute table:
Like rename "XRF_N3"in something else. It seems quite a easy issue but I don't find any information about how can I do that.
- 2,008
93
votes
7
answers
116k
views
Finding minimum-area-rectangle for given points?
As you see in the figure, the question is:
How to find the minimum-area-rectangle (MAR) fitted on the given points?
and a supporting question is:
Is there any analytical solution for the ...
- 3,337
92
votes
4
answers
177k
views
Getting coordinates from geometry in PostGIS
This line:
SELECT geom
FROM myLayer.geom
will return a hex value.
How would I get decimal values, which is a human-readable coordination?
- 1,219
89
votes
10
answers
194k
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, ...
- 1,001
87
votes
8
answers
12k
views
Managing large amounts of geospatial data? [closed]
How do you manage your geospatial data? I have terabytes of data spread out over hundreds of datasets, and have an ad-hoc solution using symbolic links within projects which link back to an domain-...
85
votes
5
answers
15k
views
Getting started with PostGIS?
I have been reading a lot about PostGIS, but I am struggling to find a good beginner's guide.
Which tutorials/books do you recommend?
84
votes
2
answers
56k
views
Difference between WMTS and WMS
What is the main difference between a Web Map Tile Service (WMTS) and a Web Map Service (WMS)?
When should you choose one over the other?
What are the (dis)advantages by choosing one over the other?
I ...
- 1,017
84
votes
5
answers
54k
views
Visualising WKT geometry string in QGIS
Is there a simple tool in QGIS to graphically visualise geometry formatted as text?
Example geometry:
POLYGON((571178 6337246,571178 6402217,598061 6402217,598061 6337246,571178 6337246))
Result:
A ...
- 4,400
83
votes
31
answers
62k
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 ...
83
votes
12
answers
207k
views
Creating point features with exact coordinates in QGIS
How do I create point features with exact (manually entered) coordinates in QGIS?
I get precise GPS coordinates from a survey team which I need to add to a point layer. What I want: add point, type in ...
- 839
83
votes
5
answers
173k
views
Getting polygon boundaries of City in JSON from Google Maps API?
When searching Google Maps for a city, the city's administrative boundary is displayed.
Is there a way to get the polygon boundaries of City in a JSON format using google maps api?
- 931
83
votes
2
answers
476k
views
Calculating longitude length in miles
Suppose I have the geographic coordinates of "Saratoga, California, USA" as
Latitude: 37°15.8298′ N
Longitude: 122° 1.3806′ W
I know from here that in the case of latitude 1° ≈ 69 ...
- 941
83
votes
5
answers
44k
views
Displaying coordinates and inputs as LatLon or LonLat?
I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it?
I think almost everyone pronounces it as "LatLon".
Who ...
77
votes
12
answers
25k
views
How much math does a GIS Analyst need to know?
For someone studying to pursue a career as a GIS Analyst, what math courses should he/she take?
Here's a long list of free Math courses from MIT to serve as a frame of reference.
Which are essential,...
77
votes
12
answers
16k
views
Alternatives to using ArcPy
I seem to use ESRI's ArcPy site package for virtually all of my Python geoprocessing. To ESRI's credit, these are an incredible suite of tools that can help accomplish a great deal. However, I would ...
- 51k
76
votes
14
answers
10k
views
What books, journals, and electronic resources are most valuable for expanding knowledge of GIS? [closed]
What books, journals, and/or electronic resources have you found most valuable for expanding your knowledge in the GIS field, and why?
75
votes
7
answers
31k
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 ...
- 973
75
votes
16
answers
10k
views
Explaining what GIS is to 11 year old kid?
Well, since it was one of the highest rated proposed questions, hasn't been asked yet, and I would love to know the answer, I thought I'd ask it.
How do I explain what GIS is for the 11 year old kid?
75
votes
6
answers
236k
views
Opening shapefile in R?
I need to open a shapefile from ArcMap in R to use it for further geostatistical analysis. I've converted it into ASCII text file, but in R it is recognized as data.frame. Coordinates function doesn't ...
- 751
75
votes
14
answers
208k
views
Running Create Extension postgis gives ERROR could not open extension control file?
I have installed PostgreSQL 9.x and PostGIS 1.5/2.0 several times and have never had this problem.
I just got a new CentOS 6.3 server up and running and and I have Postgres 9.3 functioning as ...
- 853
74
votes
3
answers
95k
views
Converting Pandas DataFrame to GeoDataFrame
This seems like a simple enough question, but I can't figure out how to convert a Pandas DataFrame to a GeoDataFrame for a spatial join?
Here is an example of what my data looks like using df.head():
...
- 1,469
74
votes
7
answers
13k
views
When to use ModelBuilder over Python scripting and vice versa?
I am new to Python scripting in ArcGIS but not new to ModelBuilder.
I would like to know the benefits of Python vs ModelBuilder.
When should we write Python script for GIS automation rather than ...
- 5,795
74
votes
5
answers
48k
views
Extracting data.frame from simple features object in R
Is there an sf-native (i.e. "correct") way of extracting everything except the geometry column from a simple features object? This works
df <- dplyr::select(as.data.frame(sf), -geometry)
but the ...
- 1,100
74
votes
2
answers
20k
views
How accurate is approximating Earth as sphere?
What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them.
Are ...
- 895