The LNDSEA1.DAT is a direct access file is a world land/sea map quantized to every 1/12 degree of both latitude and longitude. An individual bit is used to indicate whether a particular point is land or sea. The data is stored as 648 records each of which contains all of the data for a 10 degree by 10 degree square. Each record consists of 14400 (120*120) bits stored 30 bits per word (4 words per each 1/12 degree strip of data). The first word of the record indicates whether the entire 10 by 10 square is all land or water using the following definition:
-1 : square contains both land and sea
0 : square contains all land
1 : square contains all water
The next 4 words in each record are the bits for the bottom 1/12 degree
(lowest latitude) row of the 10 degree by 10 degree square with
longitude bins left to right. For each bit a 0 indicates land and a
1 indicates water. The records are ordered:
record # Latitude range Longitude range _________ _______________ _________________ 1 -90 to -80 0 to 10 2 -90 to -80 10 to 20 . . . 35 -90 to -80 340 to 350 36 -90 to -80 350 to 360 37 -80 to -70 0 to 10 38 -80 to -70 10 to 20 . . . 648 80 to 90 350 to 360
See the source code for LNDSEA function for additional information.