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Questions tagged [coordinate-system]

A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions. This tag also refers to cartographic projections and coordinate system transformations.

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263 votes
11 answers

Difference between projection and datum

What is the difference between a projection and a datum?
fmark's user avatar
  • 9,371
236 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 ...
tymtam's user avatar
  • 2,473
183 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
  • 2,186
155 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
  • 1,843
122 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
  • 4,346
108 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
  • 3,644
91 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
  • 1,021
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 ...
76 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
  • 915
70 votes
1 answer

Choosing SRID and what is its meaning? [closed]

I'm new to GIS, in PostGIS, and I'm struggling with the SRID concept. How do you choose a SRID for a database column? This is making me crazy. Why do I need to choose a SRID? What's its meaning? ...
bluish's user avatar
  • 881
65 votes
3 answers

Layers with same coordinate system should align/overlap in ArcMap but do not?

I put 4 different layers into my ArcMap document, but only one of them will show up on the map! I should be seeing the other 3 layers as well. When I do a Zoom to layer, I can see one layer, but I ...
CaliforniaGirl's user avatar
64 votes
7 answers

What strategies, criteria, or rules to use for selecting coordinate systems?

What strategies, criteria, or rules do you use for selecting coordinate systems for (a) storing, (b) analyzing, and (c) displaying GIS data? (I humbly offer my reply to a related question about ...
whuber's user avatar
  • 69k
61 votes
3 answers

Changing SRID of existing data in PostGIS?

While importing my shapefile data to PostGIS, I did not select the proper Projection. How do I now change the SRID of the data, without transforming the Coordinates?
Devdatta Tengshe's user avatar
60 votes
6 answers

One dimensional map of the world?

Bit of a strange question but hope this is OK to ask here. Has anyone heard of a '1-dimensional' projection of the world map - that is mapping all the points on the globe to a single line? I was ...
utunga's user avatar
  • 883
59 votes
6 answers

Why is the 'straight line' path across continent so curved?

This is the result of mapping the straight line path from a point in US to Poland using Distance Measurement Tool. Also, planes from Asia to US would travel almost over North Pole. Why is the path ...
Lazer's user avatar
  • 701
57 votes
7 answers

Getting list of coordinates for points in layer using QGIS?

I've got a layer in QGIS that is comprised of points. Its attribute table doesn't have (show) the corresponding x and y coordinates for each point. Is there a way for me to extract a list of ...
hpy's user avatar
  • 3,117
56 votes
4 answers

Why has Web Mercator (auxiliary sphere) become the web map standard?

I understand what the difference is between the Web Mercator projection and Web Mercator Auxiliary Sphere (WMAS). I also understand that both Google and Esri have adopted this projection as their ...
dkroy's user avatar
  • 1,368
53 votes
3 answers

Reprojecting vector layer in QGIS

I have a series of layers of lines (shapefiles) in My Project. The CRS of some are different and to merge them they all must have same CRS. When I use Processing > Toolbox > Qgis_algorithims >...
razi's user avatar
  • 531
51 votes
3 answers

Transforming Shapely Polygon and MultiPolygon objects

Is there an easy way of transforming Shapely objects (namely, Polygons and MultiPolygons) from one projection to another without having to dig around and extract coordinates by hand? In fact, I don'...
Chris Fonnesbeck's user avatar
47 votes
3 answers

Reprojecting all geometries in PostGIS table?

I created a spatial table with SRID:4326. Now I want to change total projection to SRID:32644 into a new table. The old table should remain unchanged.
Satya Chandra's user avatar
47 votes
2 answers

What's the difference between EPSG:4326 and EPSG:900913?

I am a bit confused on EPSG:4326 and EPSG:900913. I thought that they were both same. Though as I am placing my features over GMaps, which is EPSG:4326, I need to define the srsname of the WFS layer ...
Sam007's user avatar
  • 4,345
45 votes
3 answers

What is the current Web Mercator projection code?

The web mercator projection, popularised by Google Maps, seems to be given a new EPSG code every couple of years. EPSG:900913 (Google in calculator text) was an unofficial code EPSG:3785 - is the ...
geographika's user avatar
  • 14.2k
44 votes
2 answers

What is the difference between EPSG:900913 and EPSG:3857?

I'm using the QGIS google layers plugin to digitize a parcel as a shapefile. Later I want to import it to PostGIS. I know that google maps use a special 'google mercator' projection. What is the ...
Jiri Kadlec's user avatar
43 votes
2 answers

Projecting sp objects in R

I have a number of shapefiles in different CRSs (mostly WGS84 lat/lon) that I'd like to transform into a common projection (likely Albers Equal Area Conic, but I may ask for help on choosing in ...
Ari B. Friedman's user avatar
43 votes
5 answers

Reprojecting raster from 0 360 to -180 180 with cutting 180 meridian using gdalwarp

I have a geotiff raster image that has a coordinate system with longitudes from 0 to 360. The horizontal center of the image is 180 longitude. See image below: I want to transform it to EPSG:4326 SRS ...
nextstopsun's user avatar
  • 1,109
42 votes
1 answer

Is WGS84 itself a Coordinate Reference System?

I was wondering the difference between WGS84 and EPSG:4326 (see this). Can then WGS84 on its own be defined as a Coordinate Reference System? Or is it just a datum so that a Coordinate System must ...
Campa's user avatar
  • 787
42 votes
1 answer

Coordinate system for accurately calculating areas of polygons that cross UTM Zones?

I have multiple polygons, all located offshore around the UK. I am trying to calculate the areas of these polygons in square kilometres, without splitting them by UTM zone. Is it possible to do this ...
the_bonze's user avatar
  • 807
41 votes
6 answers

Shapefile PRJ to PostGIS SRID lookup table?

I was wondering if there is such a thing as an shapefile PRJ to PostGIS SRID lookup table? Something that can translate the most standard shapefile PRJ definitions into the likely SRID. When using ...
RyanKDalton's user avatar
  • 22.9k
40 votes
1 answer

Defining new custom projections in QGIS?

I'm trying to define a projection in QGIS. I want to add North America Albers Equal Area Conic. From the spatialreference site I copied the proj4 line: +proj=aea +lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-...
djq's user avatar
  • 16.1k
37 votes
8 answers

How do I convert State Plane coordinates to latitude-longitude?

Given a specific state plane coordinate system (whether NAD27 or NAD83), are there any resources to convert to latitude-longitude?
Richard Morgan's user avatar
37 votes
3 answers

What is approximate error of Pythagorean Theorem vs. Haversine Formula in measuring distances on sphere at various scales?

Many people when first trying to calculate distances between two longitude / latitude pairs ask if Pythagorean theorem works as an appropriate distance function. Most often people answer "no, the ...
Amos Budde's user avatar
37 votes
2 answers

Choosing coordinate system to store geography data for celestial coordinates

I am doing an astronomy project. I want to have the information about our images stored in a spatially enabled database. This, I would think, should be a very easy special case for GIS functions ...
SO Stinks's user avatar
  • 473
36 votes
1 answer

What is the default projection in Leaflet?

I've read an API documentation for Leaflet on its site, but I can't realize: what is a default projection to view maps? It was written about spherical and elliptical Mercator and Equirectangular - so ...
Anton's user avatar
  • 461
36 votes
4 answers

What was the rationale for the non-standard UTM zones near Norway?

UTM zones 30V, 31V, 32V, 31X, 33X, 35X, and 37X do not line up with the rest of the UTM zone grid. Why was this allowed? According to Wikipedia, UTM was developed by the U.S. Army Corps of Engineers ...
Jaime Soto's user avatar
  • 1,363
35 votes
3 answers

Why are Data Projections relevant?

Why is it useful to store data in unusual projections and datums? I understand the value of projections as output constructs, because of distortion, etc: that much is justifiable. However, I don't ...
tmcw's user avatar
  • 4,266
34 votes
1 answer

How to create an accurate Tissot Indicatrix?

A Tissot Indicatrix is useful method for communicating at a glance the kinds of distortion a given projection is prone to (in the figure below, each of the red circles occupies the same area). I've ...
matt wilkie's user avatar
33 votes
3 answers

Which function for creating a POINT in PostGIS?

When defining a Point in PostGIS, when do you decide to use which of the following? ST_SetSRID(ST_MakePoint(lon,lat),4326) ST_SetSRID(ST_Point(long,lat),4326) ST_SetSRID(ST_GeomFromText('POINT(lon ...
Nyxynyx's user avatar
  • 1,657
31 votes
9 answers

ArcCatalog says spatial references don't match between feature dataset and feature class with same coordinate system?

I have a feature dataset that is using the GCS_WGS_1984 as the geographic coordinate system. It includes a few feature classes. This feature dataset is itself in a file geodatabase that contains a ...
mindless.panda's user avatar
30 votes
2 answers

What projection appeared in the NYTimes this morning?

Perhaps not as GIS related as some, but definitely about maps. Can anyone identify the map projection that appeared in the New York Times this morning? It's not one I've seen before, and a quick scan ...
mattwigway's user avatar
  • 2,917
30 votes
2 answers

Understanding difference between Coordinate System and Projection?

Can somebody please explain what is the difference between the Coordinate system (WGS 84 for example) and a Projection (Universal Transverse Mercator for example)? What is the difference between a ...
marco's user avatar
  • 1,117
29 votes
6 answers

Defining projections for multiple shapefiles in ArcMap?

I have over 100 shape files that don't have .prj file and thus when I bring them into ArcMap 10 they show the coordinate system as unknown. I know all of the shape files coordinate system is GCS WGS ...
wilbev's user avatar
  • 1,709
29 votes
8 answers

Manually transforming rotated lat/lon to regular lat/lon?

First I should clarify I don't have previous experience with the field, so I don't know the technical terminology. My question is as follows: I have two weather datasets: The first one has the ...
skd's user avatar
  • 393
29 votes
2 answers

Calculating areal distortion outside UTM zone?

One of my colleagues is working with data that is spread across two UTM zone. The majority of the data is in one zone, with a few outliers in another zone. He would like to know what the area ...
kenbuja's user avatar
  • 5,600
29 votes
6 answers

Dealing with data that spreads across UTM Zones?

I have data that spreads across two UTM Zones GDA/MGA94 UTM Zone 55 and 56. I have layers such as a cadastre, roads, pipelines etc where I want to store measurements like lengths and areas in metres ...
Ando's user avatar
  • 3,009
28 votes
1 answer

How to assign CRS to RasterLayer in R

I have a layer with coord. ref. : NA. How can I assign coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 to coord. ref. : NA? class : RasterLayer dimensions : 127,...
Nahm's user avatar
  • 851
27 votes
1 answer

Calculating Flow Direction and Delineating Basins from Projected vs. Unprojected DEM Data [closed]

This is somewhat of a theoretical question stemming from some discussions with colleagues on the topic of implications with delineating basins with projected (e.g., Albers Equal Area) vs. unprojected (...
MapBlast's user avatar
  • 1,127
27 votes
4 answers

Calculating distortion on Equirectangular Projection

I am trying to calculate distortion so I can distort overlaying text and forms to precisely match an image of an equirectangular projection. How does one calculate the distortion at a given latitude ...
NCashew's user avatar
  • 375
26 votes
4 answers

Is there any online tool for converting coordinates between different EPSG?

Every time I want to do conversion, I need to get into the console to run proj.4. Is there any online tools for converting coordinates between different EPSG?
Harold Chan's user avatar
  • 1,637
25 votes
4 answers

Is it possible to reproject spatial data using SQL Server?

SQL Server takes an SRID when creating spatial data, but is it possible to retrieve with a different SRID translating the coordinates? For example, let's say I have a bunch of spatial polygons using ...
Rowland Shaw's user avatar
25 votes
7 answers

Spatial reference for dummies?

Can anyone recommend a good reference or tutorial that explains the principles of spatial references, projections, and coordinate systems? We are a small team of programmers working with GIS ...

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