All Questions
148,010
questions
565
votes
7
answers
487k
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 which are 6 ...
- 5,777
260
votes
11
answers
145k
views
Difference between projection and datum?
What's the difference between a projection and a datum?
- 9,311
219
votes
4
answers
218k
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 ...
- 2,303
196
votes
6
answers
485k
views
Adding Basemaps from Google or Bing in QGIS
ArcGIS Desktop has the option of using basemaps from ArcGIS Online.
Does QGIS have any such options?
- 3,191
184
votes
47
answers
116k
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 ...
180
votes
7
answers
210k
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 ...
- 9,196
167
votes
4
answers
185k
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.
- 2,026
142
votes
42
answers
19k
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
9
answers
230k
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 ...
- 1,703
141
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?
- 27.5k
138
votes
17
answers
87k
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 ...
135
votes
14
answers
62k
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)...
- 6,554
117
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?
- 27.5k
116
votes
7
answers
55k
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 ...
- 6,618
113
votes
23
answers
135k
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
8
answers
90k
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 ...
- 4,265
112
votes
7
answers
176k
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 ...
- 35.4k
108
votes
14
answers
279k
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
- 1,231
108
votes
8
answers
260k
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.
- 2,161
108
votes
4
answers
464k
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 ...
- 4,156
106
votes
5
answers
245k
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 ...
- 2,109
105
votes
16
answers
66k
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?
- 3,596
105
votes
13
answers
171k
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.
...
102
votes
4
answers
35k
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 ...
- 6,554
97
votes
10
answers
55k
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 ...
- 1,741
92
votes
26
answers
124k
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 ...
- 1,021
91
votes
7
answers
108k
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 ...
- 3,287
89
votes
4
answers
108k
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.
- 1,938
87
votes
4
answers
166k
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?
- 1,169
86
votes
8
answers
11k
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
9
answers
173k
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, ...
- 951
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 ...
81
votes
5
answers
50k
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 ...
- 4,292
80
votes
5
answers
43k
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 ...
79
votes
1
answer
466k
views
Calculating longitude length in miles
Suppose I have geographic coordinates of "Saratoga, California, USA" as
Latitude: 37°15.8298′ N
Longitude: 122° 1.3806′ W
I know from here that in case of latitude 1° ≈ 69 miles and that ...
- 901
78
votes
5
answers
159k
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?
- 881
77
votes
12
answers
24k
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
2
answers
53k
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 ...
- 947
77
votes
12
answers
188k
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 ...
- 779
76
votes
12
answers
15k
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 ...
- 50.2k
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
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
217k
views
Opening shapefile in R? [closed]
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
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 ...
- 5,777
73
votes
7
answers
29k
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 ...
- 953
72
votes
11
answers
42k
views
What Makes a Map be classed as Badly Designed?
A poorly designed map can not only look visually unappealing, but can convey the wrong message, which could lead to bad decisions being made.
I would like to ask people to post examples (that are in ...
72
votes
13
answers
188k
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 ...
- 823
71
votes
2
answers
19k
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 ...
- 865
70
votes
2
answers
13k
views
Acquiring ArcGIS-like speed in Postgis
I have been using Postgis 2.0 for 3/4 of a year now and while I really enjoy using it, excessive query processing time has rendered it basically unusable for my use case.
I tend to do heavy ...
- 1,611