I've been trying for the last couple of days to import an ascii grid file into Arcmap. However, I'm really battling to project the data. Can anyone please assist? It would be very much appreciated. I've tried defining the projection but to no avail. The data should be located at roughly the following coordinates... 29. S 26. E. Please see .asc header information below...

ncols 990 nrows 1140 xllcenter -97500 yllcenter -3237675 cellsize 25 NODATA_value -9999

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  • Would be easier if you actually say which country this data is for? – Hornbydd May 9 '14 at 13:44
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    You should not have to "import" ASCII grid files - ArcMap can load these natively and should project on the fly as well. Area there any issues if you set ArcMap data frame to the "target" coordinate system then add the grid files to the map? – Jakub Sisak GeoGraphics May 9 '14 at 16:48
  • Looking at the xllcenter and yllcenter the coordinates are really bad! It's not often they are legitimately negative and especially not the Y coordinate. Based on the cell size this should be in a projected coordinates, at a punt I'd try WGS84 UTM Zone 35 North which would put this data in The Deomocratic Republic of Congo, does that sound right? – Michael Stimson May 10 '14 at 4:32
  • @Jakub - you are right, but you have to know that target coordinate system. – AndreJ May 10 '14 at 7:23

From the lat/lon coordinates, the data should be in South Africa, near Bloemfontein:

enter image description here

The coordinates of xll and yll (lower left) might fit the South African Cape coordinate System. The proj string for it is:

+proj=tmerc +lat_0=0 +lon_0=27 +k=1 +x_0=0 +y_0=0 +axis=enu +a=6378249.145 +b=6356514.966398753 +towgs84=-136,-108,-292,0,0,0,0 +units=m +no_defs

This is NOT the official EPSG definition 22287, but rather the north-oriented one implemented in latest QGIS. I have no access to Arcgis, but you should be able to define that projection too.

The blue points are in that projection. Coordinates for the upper right corner are:

xurcenter = xllcenter + ncols * cellsize
yurcenter = yllcenter + nrows * cellsize

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