It is a false assumption that a coordinate value based on the 1927 North American Datum is less accurate than one based on NAD 83 or WGS 84. The coordinates for the same location are different. But given that the datum of the coordinate matches the datum used on the map, you will see no difference in the physical location.

By way of an analogy, imagine that a map maker had decided to express all "coordinates" on his map as the distance from the tip of the Washington Monument and another map maker had decided to use the top of the empire state building. Their "coordinates" for a given location would be different, but each map would still be an accurate representation of the area.

NAD 83 and WGS 84 are probably a better mathematical approximation of the shape of the earth than is NAD 27. If you wanted to do accurate calculations of distances and directions spanning large portions of the globe this might make a difference.

For the everyday GPS user using a handful of topo maps the important thing to do is to match the datum set in the GPS with the datum the map uses. Using the wrong datum can result in position errors of hundreds of meters.

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