Map of Pafos district in Cyprus
Map Calibration without a map grid is possible. We found in our archives a 1 : 100 000 map of the Pafos district in Cyprus from the Department of Lands and Surveys, edited 1984 and last revised 1994. On the map is no indication about the datum, nor any coordinates, not even on the borders. The only thing that we learn from this map is that the mapsquares are oriented North-South and West-East.
We wanted to calibrate this map with the help of Google Earth and searched several points that could be easily distinguished on the map and in Google Earth. We used five of these points to calibrate the map in OziExplorer. The five calibration points are shown on the map below.
The next calibrated map shows the Northern part with the wonderful Akamas peninsula, Lara and the Evretou dam and resevoir.
On the Southern part we find Cape Drepano, Coral Bay and Pafos town and harbour. These maps were calibrated as a whole in OziExplorer with the indicated five calibration points. What is encouraging is that the UTM grid lines are parallel with the map squares.
But how good is this method really?
We do not have good reference material for Cyprus, so we did the test with the electronic map of the National Geographic Institute (NGI) from Belgium, which has proven many times during several years to be very accurate. In Google Earth we find areas with high resolution images and others with very low resolution. We did the test for both types of images. We used two PCs. One with Google Earth and the other with the NGI map. Before measuring a point, we zoomed both images to about the same level and measured both coordinates in the same units: d,m,s.ss
Five points of an area with High Resolution Google Earth images.
And five points from a Low Resolution area
Translation to UTM coordinates
We translated all the coordinates to UTM with Steve Dutch's online Excel program at http://www.uwgb.edu/dutchs/UsefulData/UTMConversions1.xls
Now we can very easily calculate the differences with the formula
Err = SQRT((E1 - E2)^2 + (N1 - N2)^2)
Conclusion
Coordinates, measured in High Resolution Google Earth images, are accurate enough to be used for map calibration. The errors with Low Resolution images are much more important.
