The World Digitized read.me vs 1.3 April 1987 The World Digitized is a collection of more than 100,000 points of latitude and longitude. When connected together, these co-ordinates form outlines of the entire world's coastlands, islands, lakes, and national boundaries in surprising detail. The World Digitized is a pure data base and as such contains no programs to display the data. Because many would like a starter display program to customize with their own ideas, The World Digitized Basic Display Disk is made available to those who register their copy of The World Digitized. (See the REGSTRTN.LTR file.) Installation: The World Digitized is supplied on three 360 KB diskettes. Batch files are included to automate the transfer of data to a single hard disk under the directory WORLD. While use of a large capacity hard disk is not absolutely necessary, its presence certainly makes life a lot easier for work of this volume. The following instructions refer to making that transfer. Place Disk 1 of The World Digitized into drive A:. If your hard disk is not drive C:, edit INSTALL.BAT on A: changing every occurrence of C: to your target hard drive's designation. Then switch to your hard drive [e.g. C:] and change directory to the directory in which you want the new directory WORLD to be created [e.g. cd xyz or cd \]. You need about 1.3 MB of free space on your hard disk to make the transfer. Switch back to drive A: and execute INSTALL as follows: A: INSTALL The contents of the three World Digitized diskettes will be transfered to your hard disk. WORLD and a number of sub- directories will be created in the process. Expanding Files: For the purposes of shipping, the normal ASCII files which hold The World Digitized (.mp1 format) have been compressed into binary (.mps) formated files. You can expand the binary files into their ASCII counterparts by executing the program mpstomp1 file_name b: where: file_name is the name of a .mps file without extension or drive designation. b: is the designation of the destination drive. It may be your current drive. The result will be the newly created file b:file_name.mp1. You can use your favorite text editor to view or modify any .mp1 file. The batch file EXPAND.BAT is provided to expand all your .mps files automtically. Be sure that you have approximately 1.8 MB free space on your disk before executing this file. Again the assumed designation of your hard drive is C:. If this is not so, edit EXPAND.BAT to correct the destination drive on each line where C: is used. EXPAND.BAT takes about one and a quarter hours to run (on a vanilla IBM PC.) Concatinating Files: Expanded .mp1 text files and .mp2 binary files can be concatinated into large .mp1 and .mp2 files if you want to use more than one small section of The World Digitized at a time. You might, for instance, desire to display the coastlands, islands, lakes, and political boundries of Asia together. Asia was shipped as four separate files. They can be concatinated with the PC DOS copy command: copy as*.mp1 large.mp1 or copy/B as0.mp2+as1.mp2+as3.mp2+as4.mp2 asia.mp2 Note the use of the /B binary switch when concatinating binary files. This switch is necessary because binary data might be interpreted as the End-of-File marker (Ctrl Z) expected at the end of default ASCII files. Accuracy vs. Precision: You may be lulled into thinking that the coastal outlines included in this product are highly accurate. I wish they were! Implicit in the Real variables used to record The World Digitized data are seven or eight digits of accuracy. Go to Double Precision (which is the C language default), and you have 17 places! The latitudes and longitudes in .mp1 files are limited to 3 places to the right of the decimal, primarily to save disk space. One thousandth of a degree of a Great Circle of the Earth is 0.069 miles. (3959 mi radius * 2pi/360 deg = 69 miles/deg) The unwary might incorrectly conclude that this precision implies co-ordinate accuracy to within 365 feet! You will observe goofs in The World Digitized many times this amount. In fact extraneous points were disposed of which were separated by less than a mile. Yet although this data base may lack absolute accuracy, when viewed from a global perspective, relative to their neighbors, most of the points are suprisingly accurate. Data Formats: Three formats are used to store The World Digitized data base. .mps - binary for shipping and space saving .mp1 - ASCII, latitude and longitude with comments .mp2 - binary, longitude and Mercator y for speed and proper vertical scaling. In general, all these file formats are characterized by strings of data records representing connected points. String terminations are marked by separator records or fields which delineate the strings from each other. .MP1 File Format: variable length ASCII records Data Records field 1 latitude floating point number 2 blank field separator 3 longitude floating point number [4] optional begining with a blank comment 5 line feed end of record (LF - 10) Separator Records field [1] optional blanks[s] 2 line feed end of record (LF - 10) .MPS File Format: variable length mixed binary/ASCII records field 1 latitude 4 byte binary floating 2 longitude 4 byte binary floating [3] optional ASCII characters comment [4] optional end of string (SOH - 1) separator 5 line feed end of record (LF - 10) .MP2 File Format: fixed length (10 byte) binary records field 1 type 2 byte integer 0 - start of a new string 1 - continuation of a string 2 longitude 4 byte binary floating 3 Mercator y 4 byte binary floating