All Questions
160,404
questions
596
votes
8
answers
548k
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 ...
- 6,087
263
votes
11
answers
152k
views
Difference between projection and datum
What is the difference between a projection and a datum?
- 9,371
242
votes
4
answers
259k
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 ...
- 2,533
208
votes
6
answers
538k
views
Adding basemaps in QGIS
ArcGIS Desktop has the option of using basemaps from ArcGIS Online.
Does QGIS have any such options?
- 3,319
184
votes
47
answers
123k
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 ...
184
votes
7
answers
229k
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 ...
- 9,566
183
votes
5
answers
217k
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.
- 2,186
171
votes
8
answers
280k
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 ...
- 2,003
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?
- 28k
142
votes
42
answers
21k
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 ...
141
votes
14
answers
70k
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)...
- 6,780
138
votes
16
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
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 ...
- 6,898
123
votes
4
answers
510k
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 ...
- 4,376
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?
- 28k
117
votes
8
answers
96k
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 ...
- 4,365
117
votes
8
answers
318k
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.
- 2,261
116
votes
14
answers
301k
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
- 1,311
114
votes
23
answers
141k
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?
- 1,363
114
votes
7
answers
178k
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 ...
- 35.7k
112
votes
5
answers
274k
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 ...
- 2,269
110
votes
12
answers
186k
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.
...
109
votes
16
answers
72k
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?
- 3,654
106
votes
4
answers
38k
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 ...
- 6,780
103
votes
11
answers
61k
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 ...
- 1,831
101
votes
27
answers
150k
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 ...
- 1,111
97
votes
4
answers
187k
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?
- 1,279
95
votes
8
answers
121k
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 ...
- 3,377
94
votes
5
answers
134k
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.
- 2,048
92
votes
10
answers
215k
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, ...
- 1,031
88
votes
5
answers
184k
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?
- 981
87
votes
6
answers
57k
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 ...
- 4,450
87
votes
13
answers
228k
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 ...
- 879
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
2
answers
59k
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 ...
- 1,027
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
5
answers
45k
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 ...
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 ...
83
votes
2
answers
485k
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
79
votes
15
answers
227k
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 ...
- 893
77
votes
12
answers
26k
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 ...
- 51.4k
77
votes
2
answers
21k
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 ...
- 935
76
votes
3
answers
106k
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():
...
- 1,509
76
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 ...
- 983
76
votes
6
answers
257k
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 ...
- 761
76
votes
17
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
16
answers
11k
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
4
answers
56k
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 ...
- 1,133
74
votes
7
answers
14k
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 ...
- 5,825