QGIS Dissolve tool re-projects and rotates layer

Question

I'm trying to use QGIS (2.6.1-Brighton) to aggregate polygons according to an ID attribute.

I'm using the shapefile of school district polygons in Michigan found here:

http://www.mcgi.state.mi.us/mgdl/?rel=ext&action=sext

MI Geographic Framework School Districts (v14a) is the name of the shapefile I'm working with.

I'm trying to create a shapefile of Intermediate School Districts, which in Michigan are a level of aggregation above school districts.

I should be able to do this using the dissolve tool, as there is an ID variable in the v14a shapefile (called ISD).

However, upon doing so, the resulting polygon layer appears to have been re-projected and rotated.

Here's the input polygons:

The CRS of this layer is strange, but here's the definition:

+proj=omerc +lat_0=45.30916666666666 +lonc=-86 +alpha=337.25556
+k=0.9996 +x_0=2546731.496 +y_0=-4354009.816 +no_uoff +ellps=GRS80
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs

And here's the result of the dissolve:

With CRS:

+proj=omerc +lat_0=45.30916666666666 +lonc=-86 +alpha=337.25556
+k=0.9996 +x_0=2546731.496 +y_0=-4354009.816 +gamma=0 +ellps=GRS80
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs

Any idea what's going on here??

I would be particularly grateful if there was a way to reproject the rotated layer so as to undo the rotation, as I had already done a fair amount of stuff by hand to add new attributes to the merged layer (so that starting from scratch would require a lot of repeated manual labor).

Answer 1

Assuming you don't use the latest QGIS version (you don't mention any version in the original post), upgrade your QGIS version to 2.6.1-Brighton. I've followed the work flow you described (same data, same dissolve base field) and got the dissolved data properly located.

As to the attributes you've already appended to the result, perform a table join (find the steps here) to transfer all your edits to your properly located dissolved data. Then use "Save as..." on your joined layer to get a new layer that includes both your properly located dissolved data and your manual edits.

If there is something unclear, please tell me.