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 Jan 7 awarded Popular Question Sep 14 awarded Notable Question Jul 29 comment Defining the azimuthal equidistant projection of an Environment Canada weather radar map @whuber thank you for this useful caution. Why then would my graphical intuition be incorrect: examining the map above there have been 6 concentric circles spaced at 40 km added by the cartographer. The sixth from the centre is tangent with the map borders, implying that the borders of the map are 240 km from its centre. Understanding that a degree of latitude and longitude are not equidistant, why is not sufficient to separately find the latitude that is 240 km north of the centre point, and the longitude that is 240 km west of the centre point in order to find the top left corner? Jul 28 accepted Defining the azimuthal equidistant projection of an Environment Canada weather radar map Jul 28 comment Defining the azimuthal equidistant projection of an Environment Canada weather radar map Assuming this map is true in its alignment, then the coordinates of the corners can be found by adding or subtracting `240 km` of latitude or longitude given the centre point. Jul 28 comment Defining the azimuthal equidistant projection of an Environment Canada weather radar map A critical and very useful piece of information is evident upon zooming into the 40 km scale bar on the right. Each pixel in this GIF is square representing 1 km in dimension. It is therefore trivial to determine the corners of the map for georeferencing. The centre is at `(240,240)` in the GIF coordinate system, so each corner is therefore `339.4 km` distant from the known longlat coordinates at the centre of the map. Jul 28 comment Defining the azimuthal equidistant projection of an Environment Canada weather radar map This is very useful for defining the projection @mkennedy. What would be an efficient way to determine the coordinates of the corners of the GIF, i.e. to georeference the GIF. All I have is the scale bar on the right and,the longlat of the centre point. Features (i.e lakes) with known locations are poorly depicted. Presumably the dimensionality in km of each raster cell could be derived from the scale bar, and then the corners georeferenced using the Euclidean distance in km converted from the raster distance. Is there a more efficient way with ArcGIS? Jul 28 revised Defining the azimuthal equidistant projection of an Environment Canada weather radar map added 41 characters in body Jul 28 asked Defining the azimuthal equidistant projection of an Environment Canada weather radar map Sep 24 awarded Autobiographer Jul 2 awarded Curious Feb 21 awarded Popular Question Mar 3 awarded Yearling Jul 4 accepted Correct use of the terms geographic, path, and Euclidean distance Jul 4 comment Correct use of the terms geographic, path, and Euclidean distance Utterly comprehensive and detailed answer! I thought that cost distance calculations were typically implemented using graph theory representations of rasters. The cost distances are, then, found as the minimum weight path through a weighted graph. While this may be a typical algorithmic solution, is the approach you imply likely to be more efficient? May 17 comment Opening ArcGIS layer package in open source software? Very helpful. As indicated in your figure, the shapefiles I was looking for were in commonData\Data0 May 17 accepted Opening ArcGIS layer package in open source software? May 16 asked Opening ArcGIS layer package in open source software? Apr 30 awarded Commentator Apr 30 comment How to intersect lines and polygons in R? @Simbamangu it doesn't seem that `gIntersection()` will really do what you want. If your lines, forming a grid, were polygonized, it might work, but this is probably not what you want. I suggest asking this either on StackOverflow where more spatial R folks hang out, or on the R-sig-geo list where you'll reach the architects of `rgeos` and related tools.