Conversion Between Coordinates in Different Geodetic Datums

When merging maps created by different mapping agencies, you can observe that identical points are sometimes positioned hundreds of meters away. The reason for this positioning error can be that these agencies use different geodetic data as the basis of their coordinate systems.

A geodetic datum, or horizontal geodetic datum, is a coordinate reference system that describes the geographic coordinates of a point expressed by its latitude and its longitude. Over the years, hundreds of different geodetic data have been used by cartographers around the world. However, because the geoid surface is irregular, most of the time the same point read using two different geodetic data showed different coordinates. Nowadays, with the use of satellites and global positioning systems, geodetic surveys provide centimeter accuracy.

Because of the discrepancies from one datum to another, integrating maps coming from different sources requires data conversion.

This section shows how you can perform a datum conversion with Views Maps and presents the conversion method used.

The section covers the following topics:

• Horizontal Datum Shift

• Datum and Projections