The world is divided into 60 east-west zones each 6 o wide in longitude. Metadata , or data about data, should contain information on the datum and projection of a geospatial dataset. If metadata files follows FGDC requirements, they will contain this information. ArcView, on the other hand, will not allow the user to query the dataset to determine the projection or datum. The header of a dataset may contain the information, if the dataset has a separate header.
Headers are common for raster datasets.
A text editor can read the header. For example, a landcover vector dataset could be overlain on a DOQQ to allow comparison of features such as road intersections or permanent shorelines common to both layers. A GPS receiver that is set to a known reference system, can collect coordinates at well-defined locations, such as road intersections and those data can be overlain on the dataset in question. If the datasets are hundreds or thousands of miles apart, the projections are different. In the conterminous Unites States NAD27 and NAD83 are the two common choices for datums.