Ticket #1890 (closed bug: fixed)
Scale and ScaleLine in Google approx double correct figure at some res'ns
|Reported by:||CharlesHarrison||Owned by:||ahocevar|
|Keywords:||Inaccurate Scale Google Layer||Cc:|
I first noticed this checking out my own work.
I have a test satellite alignment calculator page that draws in the correct azimuth on two maps side by side, a Google map and a UK Ordnance Survey map. In order to check the maps against each other, I have been following the lines out 5-10km or so and then comparing their distances to a landmark. By this means, I have been able to establish that the lines agree to the order of 1-1.5 10,000ths degree, easily good enough for purpose.
However, I had one puzzling anomalous result, approximately double that, and then I noticed the Google scale was just plain unrealistic. You can recreate this by going to ...
... entering Latitude 58.15009, Longitude -5.24076, Sat 28.2E (the default) and Calculate UK Grid Variance. Then press Submit, and go out 10.3km to Loch a Mhadail.
Here's what you should see:
The loch is shaped roughly like an upside down fat T, and according to my OS hardcopy the distance across the base is 850m. The OS on-line map and scale make it about 860m (my hardcopy is 20 years old, so it could be that now, and I'll buy that), but the Google map and scale make it about 1.63km! Further, the two images of the loch are about the same size, yet the written Google scale reads 1:27K and the written OS one 1:14K!