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1500 questions
604
votes
7 answers
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 places long.
Do fewer decimal points affect…
Saurabh
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263
votes
11 answers
Difference between projection and datum
What is the difference between a projection and a datum?
fmark
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248
votes
4 answers
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 use WGS…
tmaj
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212
votes
6 answers
Adding basemaps in QGIS
ArcGIS Desktop has the option of using basemaps from ArcGIS Online.
Does QGIS have any such options?
SNT
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189
votes
5 answers
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.
Alex B
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184
votes
47 answers
Seeking examples of beautiful maps?
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 any manner.
Below I have posted one of my favorite…
Andy W
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184
votes
7 answers
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 tried the setup - express desktop install - all…
Miro
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176
votes
8 answers
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 Haversine. I could also work with a distance and a…
Thomas O
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143
votes
5 answers
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
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143
votes
14 answers
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)
Wikipedia visualizes it nicely using a rubber…
Adam Matan
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142
votes
42 answers
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 have installed?
I'm not necessarily referring to…
Radar
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138
votes
16 answers
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 outlook on web mapping solutions (both client and…
Mr_Chimp
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125
votes
4 answers
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 it is on positive side +1 for both latitude and…
kinkajou
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125
votes
7 answers
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 cluster as input. At the output function returns…
drnextgis
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121
votes
8 answers
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
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