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MAP(7)		       Miscellaneous Information Manual			MAP(7)

       map - digitized map formats

       Files used by map(7) are	a sequence of structures of the	form:

       struct {
	    signed char	patchlatitude;
	    signed char	patchlongitude;
	    short n;
	    union {
		 struct	{
		      short latitude;
		      short longitude;
		 } point[n];
		 struct	{
		      short latitude;
		      short longitude;
		      struct {
			   signed char latdiff;
			   signed char londiff;
		      }	point[-n];
		 } highres;
	    } segment;
       where  short  stands for	16-bit integers	and there is no	padding	within
       or between structs.  Shorts are stored in little-endian order, low byte
       first.  To assure portability, map accesses them	bytewise.

       Fields  and  tell  to  what 10-degree by	10-degree patch	of the earth's
       surface a segment belongs.  Their values	range from -9 to  8  and  from
       -18  to 17, respectively, and indicate the coordinates of the southeast
       corner of the patch in units of 10 degrees.

       Each segment of |n| points is connected;	consecutive segments  are  not
       necessarily  related.   Latitude	and longitude are measured in units of
       0.0001 radian.  If n is negative, then differences  to  the  first  and
       succeeding points are measured in units of 0.00001 radian.  Latitude is
       counted positive	to the north and longitude positive to the west.

       The patches are ordered lexicographically by then A printable index  to
       the  first segment of each patch	in a file named	data is	kept in	an as-
       sociated	file named data.x.  Each line of an index  file	 contains  and
       the  byte position of the patch in the map file.	 Both the map file and
       the index file are ordered by patch latitude and	longitude.

       The data	comes from the World Data Bank I and II	 and  U.S.  Government
       sources:	the Census Bureau, Geological Survey, and CIA.



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