What does NAD83 and NAD27 mean?
NAD83 and NAD27 indicate the “UTM projection”, or the “Datum”. UTM coordinates assume that the earth is flat within an area called a Zone. The calculation that allows to obtain UTM coordinates is different now (North American Datum 1983 or NAD83) than the one used during the first atlas (North American Datum 1927 or NAD27). If you are using a GPS, make sure to set your datum to NAD83. Please read your instruction manual if you are not sure how to do this. If you are using a topo map, the datum will be identified near one of the corners. Most maps in southern Ontario are now NAD83, but there are still older maps with NAD27 available, especially in remote areas.
