map.7 (1892B)
1 .TH MAP 7 2 .SH NAME 3 map \- digitized map formats 4 .SH DESCRIPTION 5 Files used by 6 .IR map (7) 7 are a sequence of structures of the form: 8 .PP 9 .EX 10 struct { 11 signed char patchlatitude; 12 signed char patchlongitude; 13 short n; 14 union { 15 struct { 16 short latitude; 17 short longitude; 18 } point[n]; 19 struct { 20 short latitude; 21 short longitude; 22 struct { 23 signed char latdiff; 24 signed char londiff; 25 } point[\-n]; 26 } highres; 27 } segment; 28 }; 29 .EE 30 where 31 .B short 32 stands for 16-bit integers and there is no padding within or between 33 .BR structs . 34 Shorts are stored in little-endian order, low byte first. 35 To assure portability, 36 .I map 37 accesses them bytewise. 38 .PP 39 Fields 40 .L patchlatitude 41 and 42 .L patchlongitude 43 tell to what 44 10-degree by 10-degree 45 patch of the earth's surface a segment belongs. 46 Their values range from \-9 to 8 and from \-18 to 17, 47 respectively, and indicate the coordinates of the 48 southeast corner of the patch in units of 10 degrees. 49 .PP 50 Each segment of 51 .RB | n | 52 points is connected; consecutive segments 53 are not necessarily related. 54 Latitude and longitude 55 are measured in units of 0.0001 radian. 56 If 57 .B n 58 is negative, then 59 differences to the first and succeeding points 60 are measured in units of 0.00001 radian. 61 Latitude is counted positive to the north and 62 longitude positive to the west. 63 .PP 64 The patches are ordered lexicographically by 65 .L patchlatitude 66 then 67 .LR patchlongitude . 68 A printable 69 index to the first segment of each patch 70 in a file named 71 .I data 72 is kept in an associated file named 73 .IB data .x\f1. 74 Each line of an index file contains 75 .L patchlatitude, 76 .L patchlongitude 77 and the byte position 78 of the patch 79 in the map file. 80 Both the map file and the index file are ordered by 81 patch latitude and longitude. 82 .SH "SEE ALSO" 83 .MR map (7) 84 .br 85 The data comes from the World Data Bank I and II and 86 U.S. Government sources: the Census Bureau, Geological 87 Survey, and CIA.