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607 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 ...
Saurabh's user avatar
  • 6,197
262 votes
11 answers

Difference between projection and datum

What is the difference between a projection and a datum?
fmark's user avatar
  • 9,381
250 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 ...
tmaj's user avatar
  • 2,613
213 votes
7 answers

Adding basemaps in QGIS

ArcGIS Desktop has the option of using basemaps from ArcGIS Online. Does QGIS have any such options?
SNT's user avatar
  • 3,389
192 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's user avatar
  • 2,276
184 votes
47 answers

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

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 ...
Miro's user avatar
  • 9,784
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 ...
Thomas O's user avatar
  • 2,053
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)...
Adam Matan's user avatar
  • 6,848
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's user avatar
  • 28.2k
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 ...
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 ...
126 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 ...
kinkajou's user avatar
  • 4,426
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 ...
drnextgis's user avatar
  • 6,938
123 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's user avatar
  • 2,321
119 votes
14 answers

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
mlo55's user avatar
  • 1,341
119 votes
8 answers

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 ...
Sam007's user avatar
  • 4,415
118 votes
13 answers

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?
matt wilkie's user avatar
  • 28.2k
114 votes
23 answers

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?
TroutSlayer's user avatar
  • 1,363
114 votes
7 answers

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 ...
blah238's user avatar
  • 35.8k
113 votes
5 answers

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 ...
stUrb's user avatar
  • 2,289
110 votes
12 answers

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. ...
108 votes
4 answers

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 ...
Adam Matan's user avatar
  • 6,848
107 votes
16 answers

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?
com's user avatar
  • 3,684
104 votes
12 answers

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 ...
Andreas Bilger's user avatar
101 votes
27 answers

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 ...
Kevin's user avatar
  • 1,111
99 votes
4 answers

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?
Kourosh's user avatar
  • 1,299
97 votes
8 answers

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 ...
Developer's user avatar
  • 3,407
96 votes
5 answers

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.
G M's user avatar
  • 2,078
95 votes
10 answers

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, ...
Vincent's user avatar
  • 1,061
91 votes
13 answers

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 ...
Per Engstrom's user avatar
91 votes
5 answers

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?
Luis Tiago's user avatar
  • 1,011
88 votes
6 answers

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 ...
Chau's user avatar
  • 4,490
87 votes
2 answers

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 ...
Edward van Raak's user avatar
87 votes
8 answers

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

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 ...
ABC's user avatar
  • 961
85 votes
5 answers

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

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

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 ...
82 votes
15 answers

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 ...
losthorse's user avatar
  • 923
79 votes
3 answers

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(): ...
atkat12's user avatar
  • 1,549
78 votes
12 answers

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 ...
Aaron's user avatar
  • 51.7k
77 votes
12 answers

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
7 answers

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 ...
mk.archaeo's user avatar
77 votes
2 answers

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 ...
Jeff B's user avatar
  • 935
76 votes
17 answers

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?
76 votes
4 answers

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(, -geometry) but the ...
eivindhammers's user avatar
75 votes
16 answers

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

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 ...
slava's user avatar
  • 751
74 votes
7 answers

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 ...
BBG_GIS's user avatar
  • 5,825

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