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I need to use this file on a map but I am not able to match the projection with the others I have, primarily data downloaded from OSM (city of Boston). I read many articles, I have repeatedly tried to change the layer CRS, convert to Shapefile but to no avail. Can anybody help?

This is the link to the dxf file:

http://www.bostonredevelopmentauthority.org/documents/planning/udtg/2d/city-blocks

  • I found two documents that state the coordinate system is NAD 1983 State Plane Massachusetts Mainland but they don't say whether to use meters or US survey feet. I couldn't get the CAD file to display to double check. If meters, Y around 900k. If feet, Y around 2900k. – mkennedy Dec 19 '13 at 16:52
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Here is a long form version of an answer that may give you some tools to solve this sort of problem on your own in the future.

First, when you are viewing file types from specific vendors, it is helpful to have their native viewer, if they offer it. In this case, the .dxf file type is created by Autodesk. They offer a free viewer called DWG Trueview. Don't let the name fool you, it also reads and displays .dxf files.

Once you have this, a first step to determining the characteristics of a file like this is to open it and look around. Since you know that this is city blocks, it gives you a frame of reference for the scale of the features you are looking at. Look at the coordinates in the bottom left, and see what they are. See how quickly they change as you move the cursor. If they change faster, it is likely they represent a smaller unit of measure, possibly feet. Here is a screenshot, that is zoomed in: DWG Trueview 01

Compare the cursor location and the coordinates to this one, and see how much they changed: DWG Trueview 02

From the amount they change, it is probably safe to assume that the units are in feet. The next step is to find a spatial reference that might match. The best place for that is here: Spatial Reference
Search for Massachusetts and see what comes up. Spatial Reference - Massachusetts

Since you are just trying to get a baseline, you can just choose the first one that lists feet. A caveat to this is that you want to choose the newer datum, in this case, NAD 83 (North American Datum 1983). In this case, you are looking for the city of Boston, so it would be logical to choose one of the Mainland entries.

Let's try the first one in the list: EPSG:2249: NAD83 / Massachusetts Mainland (ftUS)

If you open QGIS, and add the dxf layer, it will ask you to select a coordinate reference system. If you enter the EPSG code 2249 into the Filter box, you can see that it filters the list in the lower part, and the first one listed is the one you found above. QGIS Coordinate Reference System Selector - EPSG 2249

Now, you just need a reference layer to compare it to. Open Street Map is a great source for that. Their Wiki, tells you how to reference the data in QGIS. Open Street Map Wiki - QGIS

Choose one of the tiles, and load it in. If it overlays properly, you know you found the correct coordinate system, and the correct units for your data. If it doesn't, then you can go back and try a different one.
In this case, you get a nice overlay: QGIS - Dxf and Openstreetmap

The path to the solution all starts with looking at your data first, and trying to glean as much information out of it as you can. In this case, looking at the coordinates, then understanding the scale of the data, and the location all provided important clues to finding the appropriate spatial reference.

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EPSG:102686 (or should I say ESRI:102686?) fits good to openstreetmap background:

enter image description here

If you don't have it, try this custom CRS proj string:

+proj=lcc +lat_1=41.71666666666667 +lat_2=42.68333333333333 +lat_0=41 +lon_0=-71.5 +x_0=200000 +y_0=750000.0000000001 +datum=NAD83 +units=us-ft +no_defs
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    Which is EPSG:2249 – mkennedy Dec 19 '13 at 17:13

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