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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61
votes
3answers
78k views

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 ...
95
votes
16answers
51k 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?
16
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1answer
4k views

Using customized Coordinate System in ArcGIS Desktop?

I don't know so much about coordinate systems... In my office we use to deal with spatial data coming from archaeological sites. Each site has its own x-y-z coordinate system (GCS). Three simple ...
233
votes
11answers
128k views

Difference between projection and datum?

What's the difference between a projection and a datum?
40
votes
1answer
7k views

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 ...
20
votes
2answers
11k views

Displaying world country shapefiles centered on Pacific Ocean using Robinson or Miller Cylindrical projection in QGIS?

I wish to display a map in QGIS (world country shapefiles) showing all countries but centered on the Pacific area. I am not familiar with Proj4, so is there any way this can be done in QGIS?
111
votes
5answers
185k 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 ...
44
votes
3answers
57k views

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/...
174
votes
3answers
155k 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 ...
48
votes
7answers
97k views

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 ...
38
votes
6answers
20k views

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 ...
37
votes
1answer
21k views

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=-...
51
votes
8answers
100k 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 ...
31
votes
1answer
6k views

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 ...
31
votes
5answers
8k views

How to reproject raster from 0 360 to -180 180 with cutting 180 meridian

I have a geotiff raster image that has a coordinate system with longtitudes from 0 to 360. The horizontal center of the image is 180 longtitude. See image below: I want to transform it to EPSG:4326 ...
61
votes
7answers
7k views

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 ...
63
votes
2answers
14k 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 ...
17
votes
3answers
83k views

Changing projection of shapefile in QGIS?

How do I change the projection of my shapefile using QGIS? The default projection is set to EPSG:3003, I want to change it to wgs84 EPSG:32632. When I do a reprojection or I change projection in the ...
52
votes
6answers
32k views

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 ...
6
votes
1answer
2k views

Raster incorrectly reprojected to OSGB(27700)

Ubuntu 12.04, QGIS 1.8.0, GDAL/OGR 1.7.3, GEOS 3.2.2 Open a Spatialite db with OS Mastermap poly layer (EPSG:27700); Add OpenLayers Plugin (1.0) from QGIS offical repository; Add a Google Satellite ...
27
votes
2answers
8k views

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 ...
128
votes
4answers
134k 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.
51
votes
2answers
37k views

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?
25
votes
7answers
22k views

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 ...
3
votes
2answers
5k views

Getting incorrect slope values from an ASTER DEM in QGIS?

I have a DEM layer from ASTER satellite and I want to get the slope information from it. I use terrain analysis > slope, but the output is so wrong. Why is that? Here is the DEM: And here is the "...
9
votes
2answers
2k views

Why are heatmaps on qgis 2.8.1 produced in the wrong CRS?

I noticed that the heatmap calculation on the new upgrade version of qgis is given the raster map without any coordinate system. Have you got the same problem?
72
votes
5answers
39k 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 ...
21
votes
11answers
5k views

Discontinuous or Interrupted map projections?

Do any of the current open source GIS softwares support discontinous projection systems? E.g. sinusoidal, dymaxion, butterfly, etc? If not, are there any affordable commercial ones that do (affordable ...
31
votes
3answers
11k views

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 ...
13
votes
2answers
23k views

How to enable projection transformation in QGIS

My QGIS project has two layers, one layer is retrieved by Google layer plugin which fetches the static Google map image whose CRS is +proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +...
5
votes
2answers
1k views

Mapping Russia - Int'l dateline splitting polygon

I am having the issue where the International Dateline is splitting a polygon I am working with. I have a layer of the "Federal Districts" of Russia, and the eastern most federal district is being "...
39
votes
3answers
16k views

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.
14
votes
2answers
4k views

Ortho Projection produces artifacts

I`m trying to create a sphere-like view using qgis and the "world from space"-projection http://spatialreference.org/ref/sr-org/6980/ (essentialy an ortho-projection). ArcGIS wraps the shapes ...
2
votes
3answers
6k views

Local Coordinate to Geocentric

The ultimate question, I need a transformation matrix to take a point in local space representing a roughly 500m x 500m place in New Mexico centered at -108.619987456 long 36.234600064 lat. The final ...
12
votes
2answers
2k views

Where did the polygons go after projecting a map in QGIS?

I'm fairly new at GIS know-how, but I've run into a problem with a projection of a world map. I have a shapefile of all countries I downloaded from Natural Earth. After projecting it into a ...
11
votes
1answer
3k views

How to compute the bounding box of multiple layers in lat/long?

I am writing an application to performance test all kinds of map services, primarily AGS 9.x, AGS 10, and WMS 1.x. Part of the application involves generating random bounding boxes for individual ...
12
votes
5answers
17k views

How can I measure area from geographic coordinates?

If I have polygons in geographic coordinates (WGS84), how do I measure the total area each takes on the surface of the earth, taking into account the curvature of the earth?
11
votes
2answers
51k views

Changing unit of measure from degrees to meters in QGIS?

I am running QGIS 1.7.0 on windows, and I donwloaded a shapefile of census block group boundaries from TIGER. This file appears to be in the WGS 84 coordinate system, and when I open it in QGIS the ...
8
votes
1answer
4k views

Manipulating Azimuthal Equidistant Projections in QGIS

I have a shapefile of world countries that is projected as Azimuthal Equidistant with Chicago, USA as the center. I would like to change the projection such that Edinburgh, UK is the center. One would ...
6
votes
1answer
799 views

Slope analysis from NED data gives crazy histogram? [duplicate]

I'm attempting a simple slope analysis in QGIS2 using the plugin at Raster -> Terrain Analysis -> Slope. The slope output layer has a very strange histogram, basically spikes at 0 and at 89.9098 with ...
4
votes
1answer
6k views

Reprojecting MODIS Swath data to WGS84 using GDAL [closed]

Im new to GIS and now working with MODIS04L2 Aerosol Optical Thickness image. I need to reproject the image to other coordinate system such as WGS84 for later work but now Im stuck with it. I have try ...
22
votes
6answers
24k views

Moving vectors to specified coordinates in QGIS?

I have a layer of vectors located around, say, (100, 100), and I want to move them to new coordinate like (1000, 1000). How should I do it using QGIS?
18
votes
1answer
27k views

GDAL/Python: How do I get coordinate system name from SpatialReference?

In Python, using GDAL, I've extracted a raster's projection as a WKT string as follows: wkt = dataset.GetProjection() # wkt is 'PROJCS["GDA_1994_Transverse_Mercator",GEOGCS["GDA_1994",DATUM["GDA_1994"...
8
votes
3answers
6k views

Using ArcObjects to choose GeoTransformation?

I’m currently building a Desktop add-in tool with ArcObjects that: Asks a user to select a feature class Reprojects the feature class to Web Mercator Executes some geoprocessing The initial ...
5
votes
1answer
451 views

Slope layer with false results in QGIS? [duplicate]

After the DEM creation, I wanted to create slope layer. However, the result has not satisfied me. I don't think the slope map is correct. Have you ever encountered false calculated terrain map? ...
28
votes
1answer
6k views

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

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 (...
43
votes
2answers
30k views

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 ...
19
votes
1answer
5k views

File size inflation normal with gdalwarp?

After using gdalwarp to project and align-to-grid (via -tap) a number of rasters I noticed that the output rasters were significantly larger than the original rasters. A fairly thorough web search ...
22
votes
3answers
6k views

Do ArcGIS SpatialReference object factory codes correspond with EPSG numbers?

I've got a project where I'm reading in geometry objects from text files to put them in ArcSDE. These geometry objects have an associated EPSG code, and I'm looking for a way to ensure they're in the ...
4
votes
1answer
2k views

How to render area that crosses 180°?

The problem is that the Chukotka Peninsula is located in the Western Hemisphere. So it is on the left side of Natural Earth Datasets. It needs to be moved to the right. I tried to use following srs(...