How to identify the coordinate system of a shapefile?

How to identify the coordinate system of a shapefile?

If you have ArcGIS Desktop, add some reference data that covers the same area to ArcMap. This reference data must have a valid coordinate system (projection) definition. Add the data in an unknown coordinate system. Research what possible coordinate systems are used in this area.

How to convert a.shp file to a.prj file?

A quick and dirty way is to us Shp2KML and convert them to KML ( http://shp2kml.sourceforge.net/ ). Assuming that the projection is correct. Open up the prj file and see what it says. If it says WGS84, or NAD83 then you will likely be fine.

How to create a.prj file for an image?

The easiest way to create a .prj file for an image is to simply copy an existing .prj file from a shapefile or from the sample .prj files included with ArcPad on the PC (e.g. C:\\ESRI\\ArcPad 5.0.1\\Coordinate Systems).

Where does Esri Store the metadata for a coordinate system?

The ESRI Projection Engine stores the metadata for a coordinate system in a string, or in a .prj file. The string, also known as a PE string, must be continuous. A PE string is somewhat complex because many of its pieces are explicitly defined. You can define your own units, datums, and spheroids.

What happens if you change the data frame’s coordinate system?

If you change the data frame’s coordinate system, all layers that have coordinate systems will be projected on the fly to the new coordinate system. If you set the data frame’s coordinate system and the data with a known coordinate system lines up with the unknown data, the data frame’s coordinate system is that of the unknown data’s.

How to find an unknown coordinate system in ArcMap?

Start ArcMap with a new empty map and add the data with the unknown coordinate system. The data must not have a defined coordinate system. For shapefiles, it must not have a PRJ file.

Why do layers with the same coordinate system not overlap?

My hypothesis is that your 30 m shift is due to datum difference but that your original shapefiles are correctly georeferenced (each in a different projection system). If selecting a transformation does not improve your accuracy, then I would add a third layer (e.g. a basemap) and try to find out which one is wrong.

How to identify the coordinate system in ArcMap?

If the coordinates are in decimal degrees, such as between longitude -180 and +180, and latitude -90 and +90, identify the Geographic Coordinate System (datum) used for the data. Prior to version 9.2, ArcMap assigns GCS_Assumed_Geographic_1 to the data, by default.

How to check each point against each shape?

And checking each point against each shape has high complexity, but for my sample of 9000 values against ~45 shapes it ran pretty quickly: PyShp will let you read the shapefile, but won’t help you figure out if a point is in a boundary. You’ll have to combine it with something like Shapely to do the geometric calculations.

What are the coordinates of a shape column?

In this case, the Shape column’s Spatial Reference property will be Unknown or Assumed Geographic. If the features’ bounding coordinates are within the range of -180 to 180 in the x direction and -90 to 90 in the y direction, ArcGIS assumes the data to be geographic and its datum to be NAD27.

What to do when spatial reference does not match data frame?

The spatial reference of the layer does not match the projection of the data frame. Solution: Ensure that the projection information of the layer matches the other layers and the data frame. This may mean that you need to reproject a layer to match the data frame or change the projection of the data frame to match the layer.

Is there a source code for ArcGIS Shapefile?

I don’t think the source code is there, unfortunately. It’s VBA-based so only usable in ArcGIS Desktop v9.2 and possibly 9.3. It does include two shapefiles with the areas of interest from the EPSG Geodetic Parameter Dataset which could be used to narrow the possibilities.

Which is the most critical issue in dealing with map projections?

The most critical issue in dealing with map projections is knowing what the projection is and having the correct coordinate system information associated with a dataset. When the first map projections were devised, it was assumed, incorrectly, that the earth was flat.

How can I identify an unknown coordinate system?

Coordinate system information is usually obtained from the data source, but not always, as with legacy data. The technique described below helps to identify the correct coordinate system. If the coordinate system is unknown you will receive a warning message when trying to add the layer to ArcMap.