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.

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40
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7answers
2k 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 ...
32
votes
3answers
6k views

LatLon or LonLat, what's the “right” way to display coordinates and inputs?

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 ...
28
votes
11answers
7k views

Best practices for identifying the unknown coordinate system of a Shapefile

I got a Shapefile but it's coordinate system is unknown and there is no .prj file. How I can identify it now? Are there any tools that could help?
27
votes
3answers
24k 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 ...
21
votes
3answers
16k views

What is the difference between WGS84 and EPSG4326?

What is the difference between WGS 84 and EPSG 4326? It seems like for a given dataset it might be both WGS 84 and EPSG 4326.
20
votes
3answers
2k views

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 ...
18
votes
6answers
12k views

How can I define projections for multiple shape files in ArcMap 10 at once?

I have over 100 shape files that don't have .prj file and thus when I bring them into ArcMap they show the coordinate system as unknown. I know all of the shape files coordinate system is GCS WGS ...
18
votes
7answers
795 views

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 ...
18
votes
1answer
3k views

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 ...
16
votes
7answers
7k views

ArcCatalog 10.0 complains that spatial references don't match between a feature dataset and a feature class that have the 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 ...
16
votes
5answers
3k views

How do you best deal 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 ...
15
votes
3answers
66k views

Does Y mean latitude and X mean longitude in every GIS software?

Now it's been 3 days 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. ...
13
votes
5answers
16k views

Get list of coordinates for points in a layer?

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 ...
13
votes
3answers
2k views

Lon/lat transformation

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 ...
13
votes
1answer
377 views

Creating nanoscale DEM with GDAL

A bit of a strange question perhaps, but let me give you a breif explanation of the background before my actual questions: Atomic force microscopy (AFM) is a method that, in short (and to my limited ...
11
votes
7answers
356 views

Public reprojection services

Are there any free public services where I can send one point in a coordsystem and it returns the point reprojected in a specified coordinate system? I will not be doing many requests, for now it is ...
11
votes
3answers
2k views

Official term for latitude longitude coordinate system?

May I know what is the correct specific term for latitude longitude coordinate system? With "Geographic Coordinate", it seems to be a general term for every other system?
11
votes
2answers
1k views

ArcGIS Length and Area Calculation Scenarios

Trying to get a handle on how length and area are calculated in different scenarios in ArcGIS. I don't know why I can't find a answer on the feature class fields, but I can't find a precise answer, ...
10
votes
10answers
5k views

Batch convert lat longs to UTM?

I've got a .csv file that contains a long list of latitude and longitude points. Is there an efficient way to batch convert the list into a projected UTM coordinate system? Thanks.
10
votes
3answers
1k views

Is the GEO tag for QR codes lat/long or long/lat

I just found out that you can add a geographic component to a QR code. I also just found you can create one on the Google Chart API using this: ...
9
votes
1answer
579 views

How can I see the coordinate transformation parameters in QGIS?

How can I see (and edit if possible) the transformation method and parameters used by QGIS for "on-the-fly" transformation, and then for saving data in another CRS? Like in ArcGIS? Here is the ...
9
votes
2answers
1k views

How can I convert geomagnetic coordinates to geographic coordinates without doing the math myself?

I have some data which are in geomagnetic coordinates; that is, they are latitude and longitude, but in reference to the magnetic north pole in Canada rather than the geographic north pole. As you ...
8
votes
6answers
1k views

Looking for a tool to convert DD to DMS

I am looking for either an online tool or one that I can download to convert DD to DMS. For example, I want to convert from: 41.590833, -93.620833 to 41° 35′ 27″ N, 93° 37′ 15″ W ... Those are the ...
8
votes
5answers
2k views

What are the advantages / disadvantages of reporting location in decimal degrees versus degree min sec?

Many scientific articles report site location in units of degree/min/sec, but for analysis in with non-GIS software, it is easier to use decimal degrees. Is there a reason for degrees / min / sec to ...
8
votes
3answers
7k views

Coordinate System Transformation in ArcMap

For the Data Frame Properties on a map in ArcMap, what is the difference between selecting a new coordinate system and using a Transformation?
8
votes
3answers
477 views

Distance measurements across UTM zones: use geographic or planar approaches?

I have a survey grid spread across 3 UTM zones (36N, 36S, 37S). I want to find the nearest (or shortest) distances of the centroids of these grids to roads and various points between. It seems like ...
8
votes
2answers
312 views

Problem with plotting map in R

While plotting the gadm map of Russia in R, I have a problem at the 180 degree meridian, where part of the Russian region is plotted separately. You can see it on the plot using the following code ...
8
votes
3answers
326 views

Global grid, which reference system to use?

I have seen a couple global studies using WGS84 as geographic reference, with the problem that the area of raster cells is not constant. Which reference system would you use for a global analysis in ...
8
votes
1answer
234 views

Reprojection - Learning the ins and outs

I would like to expand my knowledge coordinate systems, projections and reprojecting data, with a view of writing a reprojection engine. Could you provide me with some resources (books, websites, ...
8
votes
1answer
2k views

getExtent() in OpenLayers returns strange values

I'm trying to get the bounding box of the map area displayed by OpenLayers. I tried to use map.getExtent() because it should be exactly what I need, but the returned values are "strange": For ...
8
votes
2answers
2k views

Measuring distance in spherical Mercator vs zoned UTM

I've got points in WGS84 lat/long and I'd like to measure "small" (less than say 5km) distances between them. I can use the haversine formula from http://www.movable-type.co.uk/scripts/latlong.html ...
8
votes
1answer
1k views

Computational most efficient way to convert Cartesian to Geodetic Coordinates

As far as I understand the literature there are several ways to convert a set of geoecentric cartesian coordinates to geodetic coordinates Bowring, 1976 Borkowski, 1989 Lin & Wang, 1995 Toms, ...
8
votes
1answer
1k 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 ...
8
votes
2answers
984 views

Nearest point on a line ( Spherical / Mercator projection )

I have a line (Ax,Ay - Bx,By) over a mercator projection (google maps) and a random point (Cx,Cy) nearest to that line, i would to know the closest point (transparent blue on the image) over that line ...
8
votes
3answers
640 views

Longitudinal Issues with NetCDF data

I am seeking advice on working with world data sets where the GCS has a positive range (0 degrees to 360 degrees). The data I am working with are NetCDF oceanographic data and have positive coordinate ...
7
votes
3answers
4k views

Geodetic Coordinates And Latitude, Longitude

Would it right to say that geodetic coordinates (phi & lambda) are the same as latitude & longitude?
7
votes
1answer
171 views

Can I just swap out a .prj file to reproject a shape file?

I'm an experienced software developer -- but a GIS noob. I have a shape file that I am trying to turn into a SVG map with Kartograph. When I try to run Kartograph I get this error: ERROR 6: No ...
7
votes
2answers
129 views

Which SRS to use for global distance queries?

I have a database with a lot of points in WGS84. Now I am building an cache that performs NN and points in range queries using a KDtree. The point [sic] is that the search radius will be provided in ...
7
votes
1answer
116 views

Using customized Coordinate System for Archaeological site data

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 ...
7
votes
2answers
375 views

How to Georeference Photos With No Spatial Reference?

I have about 100-200 field ground shot photos I would like to overlay in ArcGIS 10 that have no spatial information which I need to somehow develop using a photogrammetric formula. The camera was ...
6
votes
4answers
450 views

Where should I start advanced GIS learning

I am relatively familiar with most of the GIS stuff. I develop GIS applications as well with open source offerings. Still I find some lapses in my theoretical knowledge in GIS. What resources can you ...
6
votes
7answers
2k views

How can I digitize a PDF image?

I have an image file in pdf format which includes some drawings (lines, closed areas, and points). I want to digitize it into a shapefile so that I can show it on a Google map. I have a couple of ...
6
votes
3answers
287 views

How does ArcGIS determine which transformation to use when projecting on the fly?

How does ArcGIS determine which transformation to use when projecting on the fly? Where this would come in would be going from NAD 83 to WGS 84. Multiple transformations could be considered so how is ...
6
votes
2answers
698 views

Why do my Shapefiles not align correctly?

First: I'll summarize what I understand so far so please confirm or correct me. When On-the-Fly is selected a layer is re-projected from that of the layer's CRS to that of the project CRS, IF ...
6
votes
2answers
4k views

How do I convert affine coordinates to lat/lng?

I am extremely new to GIS. I'm using gdal to read in a landuse/landcover map and I need to pick out the lat/lng of certain land cover types to index into a different dataset which is expressed only ...
6
votes
2answers
358 views

What does coordinate system WG 21° mean?

I have a land survey document for a piece of land, it contains absolute coordinates that I would like to locate on google maps, but I don't know how to correctly interpret the data. What does the ...
6
votes
1answer
9k views

QGIS - Change unit of measure from degrees to meters

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 ...
6
votes
1answer
915 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 ...
6
votes
1answer
319 views

Coordinate system in aerial imagery

I am calculating WGS84 coordinates of points in an aerial image, given the WGS84 coordinates of the center of the image and the ground distance width and height (calculated from altitude and lens ...
6
votes
1answer
958 views

Difference between Geographic-3D and Geocentric CRS

I'll start with the OGP definitions: Geographic. A coordinate reference system based on a geodetic datum and using an ellipsoidal (including spherical) model of the Earth. This provides an accurate ...