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Excuse me for a simple question. I have CSV files of X,Y data (in decimal degrees) that I want to add to a map and view with a shapefile of level III ecoregions that I downloaded from the USGS website. Seemingly very simple I know, but when I add the points using "Add delimited text layer" and used the closest coordinate system I could find to the USGS shapefile the two layers do not line up. In argis I remember when adding X,Y data you could define the coordinate system of the new file based on the coordinate system of another existing shapefile rather than selecting from a list and hoping that the right one is there. Is there a way to do this in QGIS? I obviously dont know much about GIS software, and this is the #1 biggest problem I have with getting started on any project - making the coordinate system of two files match up! I would so appreciative if someone could help get me started! Thanks in advance. Sorry if my question is unclear or jumbled.... again the novice thing.

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I have a feeling you would have the same problem in ArcGIS. Set the coordinate system to what the data is in, not to what you want it to be. That's assuming the USGS data is not using a geographic coordinate reference system. In other words, assign a geoCRS to the XY data (like NAD83 or WGS84). –  mkennedy Nov 14 '12 at 18:16
    
mkennedy wrote the book on ESRI coordinate systems, literally. +1! :) –  Mintx Nov 14 '12 at 18:45
    
Thanks mkennedy. How do I figure out what coordinate system the data is in? Many of the points came from Google Earth so tried to use WGS84 but again the two layers dont overlay properly. The USGS data has associated metadata that tells me the shape file is in USA "Contiguous Albers Equal Area Conic USGS version" and "D North American 83" (NAD83?). So, the two layers do not need to have the same map projection and/or geodetic model in order to jive? I took a couple of classes on GIS and I am frustrated that this still is my achilles heel! –  Zach Nov 14 '12 at 20:43
    
@Zach Do you have access to ArcGIS too? –  Aaron Nov 15 '12 at 0:04
    
from the sound of it your shapefile has a .prj file so QGis will work it out for you - for your csv file you probably want to select epsg:4326 (WGS84) as you say it is in degrees. Make sure you have reprojection on the fly turned on. –  iant Nov 15 '12 at 8:56

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