Test 1.4: Position on Land
MEDS implementation of this test makes use of a file which contains the depth of water at every 5 minutes of latitude and longitude. The depth values are referenced to the exact 5 minute value (i.e. 5 minutes, 10 minutes, 15 minutes and so on) of the latitude and longitude. MEDS implements this test in an interactive graphics program so that a technician will be alerted that a given station location has failed the test and can take appropriate actions.
The bathymetric data are organized in an indexed file to permit rapid access. The primary key is the one degree square of the depth. When checking the position of a station, the first step is to locate the one degree square in which it lies. The depths are then retrieved for the appropriate one degree square of the station (depending if the station is close to a boundary of one degree squares, then adjacent squares are retrieved). Then the four closest five minute locations are determined which surround the station. Next the additional 12 closest five minute locations are determined. That is, the location of the station is surrounded by the sixteen closest depth values from the five minute bathymetry file. The depth of water at each of the five minute locations is tested to see if it is greater than zero (locations on land are given a value of zero in the five minute file). If 15 of 16 five minute locations have depths greater than 0, the station is decided to be in the water and the test is passed.
The five minute file used by MEDS does not include certain inland seas. Before the test is applied, stations located in the Aral Sea, Caspian Sea and Great Lakes are excluded. The following table gives the latitude, longitude boundaries used to exclude stations.
| Name | Latitude | Longitude |
| Great Lakes | 40-50N | 75-95W |
| Aral Sea | 42-48N | 58-62E |
| Caspian Sea | 35-48N | 45-55E |