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506
votes
7answers
428k 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 ...
244
votes
11answers
136k views

Difference between projection and datum?

What's the difference between a projection and a datum?
185
votes
3answers
173k 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 ...
184
votes
47answers
106k 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 ...
170
votes
7answers
176k 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 ...
164
votes
5answers
366k 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?
144
votes
4answers
150k 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.
142
votes
42answers
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 ...
138
votes
17answers
84k 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 ...
136
votes
5answers
26k 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?
126
votes
13answers
52k 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)...
125
votes
6answers
199k 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 ...
114
votes
13answers
7k 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?
107
votes
8answers
80k 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 ...
106
votes
25answers
123k 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?
106
votes
6answers
168k 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 ...
106
votes
7answers
48k 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 ...
101
votes
16answers
56k 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?
95
votes
12answers
244k 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
95
votes
13answers
134k 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. ...
94
votes
4answers
411k 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 ...
91
votes
4answers
31k 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 ...
91
votes
5answers
194k views

Calculating polygon areas in QGIS?

How do I calculate areas of an area shapefile in square meters or in acres (ha)? I didn't find that functionality in the vector tools.
89
votes
3answers
212k 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 ...
89
votes
9answers
47k 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 ...
85
votes
5answers
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?
83
votes
28answers
58k 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
8answers
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-...
79
votes
7answers
86k 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 ...
78
votes
24answers
96k 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 ...
77
votes
12answers
21k 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,...
76
votes
14answers
9k 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
16answers
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
5answers
40k 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 ...
74
votes
3answers
81k views

Renaming attributes/fields in shapefile attribute table using QGIS?

I would like to rename some fields in my attribute table: Like rename XRF_N3in something else. It seems quite a easy issue but I don't find any information about how can I do that... I've QGIS 1.8 in ...
72
votes
11answers
12k 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 ...
72
votes
11answers
38k 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 ...
71
votes
7answers
12k 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 ...
71
votes
2answers
44k 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 ...
70
votes
4answers
143k 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?
70
votes
1answer
428k 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 ...
69
votes
6answers
177k 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 ...
69
votes
4answers
41k views

Visualising WKT geometry string in QGIS

A very simple question: Is there a simple tool in QGIS to graphically visualise geometry formatted as text? Example geometry: "POLYGON((571178 6337246,571178 6402217,598061 6402217,598061 ...
69
votes
7answers
4k views

Are there any attempts to replace the shapefile? [closed]

Recently I've been spending a lot of time converting perfectly good field names like "Percent of citizens age 25 and over with a bachelor's degree or higher" into things like "edbchogtr" to meet the ...
67
votes
8answers
124k views

Converting projected coordinates to lat/lon using Python?

I assume this is a basic question but I can't seem to find or recognize the solution. This site returns Point: X: -11705274.6374 Y: 4826473.6922 when you searching with the first key value of ...
67
votes
6answers
24k 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 How to create regular point grid inside a polygon in ...
65
votes
5answers
45k views

Building effective heat-maps?

Using ArcGIS, QGIS, Grass, and/or GVSIG: What are some of the tools and processes involved in building effective heat maps? What are the plugins involved? What are the major data requirements? What ...
64
votes
2answers
16k views

How accurate is approximating the Earth as a 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 ...
64
votes
12answers
148k 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 ...
64
votes
5answers
100k views

Seeking Mobile GIS applications for Android Tablets? [duplicate]

I know that ArcGIS is available for Android, but does anyone know of any other GIS apps that are available for Android tablets?

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