A map projection is any method of representing the surface of a sphere or other three-dimensional body on a plane
18
votes
8answers
4k 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?
12
votes
3answers
5k views
Layers having the same coordinate system should overlap, but they don't. What's wrong?
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 ...
34
votes
5answers
3k 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 ...
35
votes
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 ...
89
votes
8answers
16k views
What's the difference between a projection and a datum?
What's the difference between a projection and a datum?
18
votes
1answer
780 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 ...
13
votes
6answers
4k 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 ...
13
votes
1answer
1k views
How to define 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 ...
4
votes
4answers
3k views
How to reproject base layers in OpenLayers?
The issue is:
I have vector/topo/image tiled maps for some places in north america which were published as ArcGIS Server REST service. These maps (A) are based in EPSG26912 projection. Now I wanna ...
19
votes
9answers
1k 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 ...
40
votes
8answers
1k views
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 ...
13
votes
1answer
2k 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 ...
11
votes
5answers
3k 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?
9
votes
3answers
4k views
How does ArcGIS compute the distance between two points with a non-equidistant projection?
This is a follow-up question to my previous one, Can you suggest some well-written introductory texts about coordinate system projections?
Let's assume I'm working with the CH1903 map projection, ...
8
votes
3answers
728 views
What is the right solution (and map projection) to compute distances between points located all over the World?
After my study on map projection I realized that it is very difficult to choose a projection that allows to compute simultaneously the distances between a great deal of points if these points are ...
6
votes
2answers
2k views
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 an object as a different spheroid?
For example, let's say I have a bunch of spatial polygons using SRID 4258, but ...
5
votes
3answers
2k views
Why don't my Shapefiles and OSM data overlap in Quantum GIS?
So I'm pretty new to GIS, and I'm working on a mapping project using data for Vancouver, Canada. I want to combine Open Street Map data along with data provided by the City of Vancouver. But the City ...
11
votes
3answers
1k 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 ...
5
votes
1answer
846 views
Mercator projection: problem with latitude formula
I'm trying to get the position of a coordinate on this map (source Wikipedia):
If I'm correct than the formula for the position of the latitude would be:
R * ln(tan(pi/4 + latitude / 2))
But ...
3
votes
1answer
494 views
Is there a simple way to compute the UTM Zone from a lat/long point?
I am trying to convert a latlong point to UTM. To define UTM projection, I need to calculate zone for the point. I am trying to figure out the best way to do this. One way to do this would be use ...
8
votes
1answer
206 views
An example Tissot ellipse for an Equirectangular Projection?
I am trying to calculate distortion of an equirectangular projection via Tissot indicatrices. I have tried following the directions on this post (among other things) but it is beyond my understanding ...
7
votes
2answers
247 views
How to determine projection parameters when customizing a projection
I am trying to customize an Albers and a Hotine Oblique Mercator (HOM) projection to minimuze distortion in the region I am analyzing. The region extends from about 51 to 62 degrees latitude, covering ...
4
votes
2answers
703 views
Projected maps don't overlap
I am very new to arcGIS and so apologise if this is a really simple question, but it has had me (and what I can find on the internet beat for 2 days now.
I am trying to build a series of layers of ...
9
votes
9answers
4k 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.
3
votes
3answers
486 views
Convert an arbitrary meta-data-free map image into QGIS project
My background: experienced programmer, amateur historian, complete beginner to GIS (so I'm using QGIS). I did learn to use the QGIS georeferencer tool though.
The input: suppose I have an image like ...
2
votes
2answers
2k views
Why does QGIS scalebar show a wrong scale?
I'm using QGIS 1.7.1 and have added a scalebar. The scalebar usually displays in degrees, unless I switch the map's projection to meters, in which case the units are display in cm. This is not ...
33
votes
3answers
8k views
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 ...
15
votes
5answers
5k views
Map projection in OpenLayers
I want to overlay some data whose projection is WGS-84 on Google map layer in OpenLayers. But I just can't make them in the right place. I did as follows:
map = new OpenLayers.Map('map', {
...
17
votes
5answers
962 views
Simplifying geometries (generalization)
What are the recommended ways of simplifying geometries? Keeping in mind projections, and simplifying state geometries for example.
I've heard about converting to an 'equi-distant' projection that ...
4
votes
3answers
468 views
How do I specify a CRS for a fictional game map in QGIS?
I am about to start playing a steampunk RPG game called The Iron Realm, which uses a fictional world map. I have recently started using QGIS v1.7 and have no real experience with GIS sysstems. I have ...
11
votes
2answers
779 views
Calculate distortion outside a 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 ...
4
votes
1answer
4k views
Openlayers and Geoserver: OSM/Google Maps and WMS Overlay
I am experiencing projection problems with the following set up:
GeoServer with ESPG:4326 based shapefiles (*.shp)
OpenJump to edit my shapefiles
Openlayers with EPSG:900913 base layers
GeoServer ...
12
votes
4answers
1k views
Does Re-Projecting an ESRI ShapeFile only update the content of the .prj file?
if i wish to change the projection of some shapefiles from .. lets say NAD83 (4269) to WGS84 (4326) ... and by using some 3rd party app .... does this mean the .prj file is only updated .. and not the ...
6
votes
5answers
2k views
Better Distance Measurements in Web Mercator Projection
I am working with an ESRI stack, storing my layers in a sql-spatial-enabled-SDE- geodatabase (Geometry type, Web Mercator-3857).
I am building a web mapping application, so by default, the tiles are ...
5
votes
2answers
1k views
How is EPSG:4326 data 'projected' in a 2D map?
I like to think I'm relatively well-versed in datums, projections, and coordinate reference systems, so if this is a stupid question I will suffer eternal shame.
OpenStreetMap data is stored in WGS84 ...
3
votes
1answer
56 views
What is displayed when I am using a geographic CRS for my project
I understand that each geographical dataset has a CRS, and that in order to overlay them, you need to either make sure that all datasets use the same CRS, or re-project some of them (or use on-the-fly ...
3
votes
1answer
174 views
Get the geotransform in Mercator given a pixel size away from the origin
I have a radar image with the following information:
The projection is Mercator (Mercator_1SP in GDAL)
The projection origin is 0º lat 0º lon
At a given geographic coordinates (e.g. lon=10º ...
2
votes
1answer
86 views
Is there a difference between ESRI's NAD83 Indiana SPW and QGIS's?
It seems ESRI and QGIS don't have the same definition for my most commonly used projection, NAD83 StatePlane Indiana West (US ft). When I create data in an ESRI product the projection shows up in ...
1
vote
0answers
109 views
How to overlay 3 different layers using ArcMap
I have to overlay 3 different layers called "Bacino Isonzo Perimetro", "Bacini Tributari Isonzo", and "Isonzo" in ArcMap. Layers'properties are shown below.
BACINO ISONZO PERIMETRO
Data Type: File ...
0
votes
2answers
65 views
WFS reprojection problems
In geoserver i have a layer in EPSG:4326.
In OpenLayers i add it on map as WFS:
markerLayer = new OpenLayers.Layer.Vector('Markers',{
strategies: [new OpenLayers.Strategy.BBOX()],
...
0
votes
2answers
520 views
How would I convert this point to WKID 4326?
This is a point in Brewster, MA, USA. How would it be converted to WKID 4326?
324299.3348436486, 832511.5939650714
16
votes
9answers
355 views
Can you suggest some well-written introductory texts about coordinate system projections?
Even after some time working in this GIS field, I still don't have a solid understanding of spatial references, how they are projected, and most importantly, if you still need to worry about the fact ...
30
votes
4answers
3k views
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 ...
19
votes
2answers
402 views
What projections should I use to make my own Globe?
Searching for an answer to this question, I found instructions posted by Gulf of Maine Research Institute showing how to create a globe.
Using manual methods ...
What approach would I take to ...
4
votes
2answers
1k 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 ...
27
votes
3answers
802 views
What coordinate system should be used 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 ...
15
votes
6answers
9k 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 ...
19
votes
3answers
343 views
Why are Data Projections relevant?
Sorry for my ignorance - especially after being in this area for a long time.
Why is it useful to store data in unusual projections and datums? I understand the value of projections as output ...
14
votes
1answer
764 views
How does one calculate 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.
So, how does one calculate the distortion at a given ...
6
votes
2answers
2k views
Derive WGS84 Longitude & Latitude from British Northings & Eastings
I'm looking for a fairly simple way to append columns with WGS84 longitude and latitude to a table containing northings and eastings. The source data is Ordnance Survey's CodePoint Open, which I is ...
