I have a tif file and (in the same folder) an accompanying tfw file that is supposed to get the right coordinates for the tif file . But when I open the tif file in Arc-map it does not show the right coordinates, in fact the reference system is "undefined". How do I get the right reference system for my tif file? I am new to Arc-map so a little help would be wonderful!
By default, ArcMap reads the TIFF header for coordinate information. However, you can overwrite this by going to Customize > ArcMap Options > Raster tab > check the option 'Use world file to define the coordinate of the raster'.
Besides the suggestion by Jake Skinner, I would check to see if the imagery actually already has a projection assigned. Use ArcCatalog to check the properties. My guess given your symptoms is that it does not. The world file( tfw) often only provides the correct location if it was already in the correct projection. Since it likely has no projection....
Chris Donohue, GISP
To expand on Chris' answer a little bit, a world file describes the cell size, any rotations, and the coordinates of the lower left corner of the raster. Here's an example from Wikipedia:
There's no information on the coordinate system, and it could be any UTM zone, a bunch of Gauss-Kruger zones, and probably a few other things. There's no way to know, unless the coordinate system is also defined in the TIFF, you have knowledge of the coordinate system, or can pick a likely coordinate system based on your knowledge of the location that the data represents.