THE MAP

1. The Micro World Data Bank in Polygons

The Amiglobe map has been taken from the Micro World Data Bank, which is a world map made of vectors. This makes easy for Amiglobe to zoom and to navigate everywhere on the map.

Here is the documentation that comes with the archive downloaded from Internet.

INTRODUCTION

The full WDB-II is a digitial map data base produced by the Central Intelligence Agency (CIA) and distributed by the National Technical Information Service (NTIS), U.S. Department of Commerce, 5285 Port Royal Road, Springfield, VA, 22161 (U.S.A.). Micro WDB-POLY is a highly compressed version which is suitable for use on micro computers and was put in this configuration by Micro Doc as Micro WDB-II. Global Associates, Ltd added new data (primarily from Charles Culberson), made various fixes to Micro WDB-II, and rearranged the data into closed polygons. Before describing Micro WDB-POLY a few words should be said about the source file - WDB-II. The following paragraphs are paraphrased from the NTIS overview of WDB-II.

WDB-II is a digitial representation of the world coastlines and boundries suitable for use in automated mapping systems. It contains approximately six million discrete geographic points and was digitized using all available sources of information. Map scales used range from 1:750,000 to 1:4,000,000 with a nominal scale of 1:3,000,000. These points are grouped by and identified as describing (1) coast lines, (2) country boundries, (3) state boundries (USA only), (4) islands, (5) lakes, and (6) rivers. Each of these groupings is further broken down into features and subordinate classifications/ ranks. These ranks are hierarchically structured, and are also used for plotting symbol definition.

WDB-II, as provided by NTIS, is in a 20 character format on five 9 track EBCDIC one-half inch magnetic tapes. This data base consists of two types of records, one for the line segment identifier data, and the other for the latitude and longitude values of each discrete point making up the line segment. In this format latitude and longitude values are recorded only as integers in degrees, minutes, and seconds. WDB-II is available for $660.00 (Order Number PB-271 874 SET/HBG).

Clearly, WDB-II is an excellent data source when making large (4 x 6 foot) plots on a mainframe or minicomputer. It is, however, somewhat large (150 - 200 megabytes) for use on microcomputers. Even on the larger commercial online graphics systems, many points have to be filtered out before generating displays. For this reason many people have spent considerable time over the past to filter and compress this data into a form which could be used in desktop computers. To these people we wish to express our appreciation - particularly Antonio Riveria who provided us with a copy of the latest download of the file.

The WDB-II product from which MWDB-POLY is derived may no longer be availiable. The CIA has replaced WDB-II with a RELATIONAL version. Contact Micro DOC (listed near the end of this document) for more information on the 1995 Relational WDB-II CD.

BACKGROUND

The present version began as a three megabyte ASCII text file which contained some 318,568 points selected from all six of the line types described above. This file was then converted into a sixteen bit integer format which reduced the size to just over one megabyte. The file was divided into six files - one for each of the six line types then the Internal Political Borders were broken down into 4 separate files. The file was configured such that it could be readily moved to most desk top microcomputers. The following table provides a brief statistical overview of the six line types which are contained in the data base.

Micro WDB-POLY File Composition

Detail level	PCOAST.PNT	PBORDER.PNT	PUSA48.PNT	PCANPROV.PNT	PMEXICO.PNT	PAUST.PNT	PISLAND.PNT	PLAKE.PNT	RIVER.PNT	TOTAL
1	22917	49073	6624	4978	879	1975	20309	4671	11146	122572
2	27775	56754	6383	5714	997	2350	24190	5758	13217	143138
3	4314	10163	1478	1113	181	634	3832	791	1817	24323
4	3033	7237	917	778	113	419	2970	581	1254	17302
5	890	4019	740	418	1984	187	1618	617	760	11233
TOTAL	58929	127246	16142	13001	4154	5565	52919	12418	28194	318568
lines	8	175	52	12	36	7	364	73	196	923

The above table shows the number of points which are in each file and for each level of detail. It also shows the number of line segments in each file.

Detail level 5 produces the least detailed graphics image. The points at each level of detail are additive to the points at all lower levels. For example, when using detail level 4 the points from both levels 4 and 5 must be used/retrieved. Therefore, if one were drawing lake lines at detail level 4, a total of 1198 (581 + 617) points would be processed. These 1198 points will describe 73 polygons. Note that the same number of polygons exist at all levels of detail. For example, regardless of which level of detail is selected, there will always be 73 polygons described by the lake data file.

Actual use of the data in these files has shown that most displays which cover a reasonably large area do not need all of the detail provided at level 1. A large area would be a major portion of the U.S.A. For large area plots level 3 or 4 is normally sufficient and greatly reduces the number of points which must be processed.

MICRO WDB-POLY FILE AND RECORD STRUCTURES

All Micro WDB-POLY files are sequential files composed of fixed length six byte records which can be accessed randomly. Each record is composed of three 16-bit signed [short] integer fields which can be read by all microcomputer languages. There are no record seperators used in these files. The record layout is:

| Code | Latitude | Longitude |

Within the Micro WDB-POLY files the records are stored as shown below. In some cases there may be hundreds of points in a single line segment. In other cases there may be consecutive header records which locate individual points to be plotted.

The same format is used for both the line header records and point records. The usage of each field is as follows:

FIELD DEFINITIONS

CODE - Line Header Records.

The CODE field is used to:

1. Identify the type of line segment which is described by the point records which follow it,

2. Identify the line or point within the line type, and

3. Provide the coordinates if the record describes a point.

In header records the CODE field is always a positive four digit number in the form of: ABBB where

A = BBB = CODE = 1 = Coast lines 001 -> 008 1001 -> 1008 2 = International Borders 001 -> 175 2001 -> 2175 4 = Internal Political Borders (001 -> 107 4001 -> 4107) U.S. 001 -> 052 4001 -> 4052 Canada 053 -> 064 4053 -> 4064 Mexico 065 -> 100 4065 -> 4100 Australia 101 -> 107 4101 -> 4107 5 = Islands 001 -> 364 5001 -> 5364 6 = Lakes 001 -> 073 6001 -> 6073 7 = Rivers 001 -> 196 7001 -> 7196

CODE - Point records.

In point records the CODE field contains the detail level. The detail level is a value in the range of 1 through 5. To properly retrieve points at any detail level use the following comparison:

IF CODE >= DESIRED_DETAIL_LEVEL THEN ...

LATITUDE and LONGITUDE - In both header and point records.

The latitude and longitude fields contain the coordinate values expressed in signed minutes. The values in these fields are computed with the formula COORD_VALUE = (Degrees * 60) + Minutes. Thus, the ranges of coordinate values in MWDB-POLY are:

90 00N = 5400 90 00S = -5400 180 00E = 10800 180 00W = -10800

NOTE: The Latitude and Longitude data can be converted on the fly to Decimal Degrees by dividing the signed minutes values by 60.

MWDB-POLY uses the standard four quadrant cartesian coordinate system in which north, south, east, and west are referenced to the equator and the Greenwich meridian.

When a header record is followed by point records the coordinates in the header record are the beginning of the line. When a header record is followed by another header record then the coordinates in the header record should be plotted as a single point. When working at low levels of detail it is common to find multiple consecutive header records which locate isolated points. This documentation and the associated files are placed in the public domain and may incorporated into other products without fee so long as appropriate credits are included. An appropriate credit line would be - "This product contains/uses data originally placed in the public domain by Fred Pospeschil and Antonio Riveria that has been modified by Paul Anderson of Global Associates, Ltd. The Original coordinate data was created by the Central Intelligence Agency."

MWDBPOLY.ZIP CONTENTS

MWDBPOLY.ZIP contains a MWDBII database that is reasonably up to date, clean, and modified to provide closed polygons without using an index file (Index files ARE available).

The following files are in MWDBPOLY.ZIP:

GLOBAL.TXT - About Global Associates, Ltd. GOODEIHS.BAS - Quick Basic program that draws Goode's Homolosine projection interrupted for continental unities. The Plot file routines and the way the map is drawn inside the "extensions" are NOT the best, but it works. The plot files import into Corel Draw with no problems. NOTE: The Open file statements will have to be modified to reflect where the *.PNT files are located on your system. This program was written for Quick Basic 4.5, however, it will run (slowly) with the Qbasic interpreter that comes with MSDOS. MWDBPOLY.TXT - This document.

PBORDER.TXT - Notes on PBORDER.PNT and VECTOR graphics output.

PCOAST.PNT - Use this file when you don't want Political Borders. PBORDER.PNT - Use this file in place of PCoast.pnt when you want political borders.

PUSA48.PNT - USA internal Political Borders.

PCANPROV.PNT - Canadian Internal political Borders.

PNTCONV.ZIP - Two programs that can be used to convert the *.PNT files to and from ASCII.

PMEXICO.PNT - Mexican Internal Political Borders

PAUST.PNT - Australian Internal Political Borders.

PISLAND.PNT - Islands of the world.

PLAKE.PNT - Lakes of the world.

RIVER.PNT - Rivers of the world. Original MWDB II file (No Polygons).

SELECT.EXE - This program is from the original MWDB II distribution disks. You can use it to: 1) Combine all the *.pnt files into 1 (one) file. Or 2) Create *.PNT/*.MAP/*.ALL or *.CCI files containing less data.

MWDB-POLY can be used AS IS with the following programs: 1) Charles Culberson's VersaMAP 2) Philip Voxland's WORLD 3) Daan Strebe's GeoCART 4) Scott Loomer's MicroCAM and WinCAM

FINAL NOTES

This document is a modified version of the original that is included with the Micro WDB-II database. Additional map data base products may be obtained from:

Micro Doc (Fred Pospeschil) 3108 Jackson St. Bellevue, NE 68005

- and -

Charles Culberson 8 Ritter Lane Newark, DE 19711

The MWDB-POLY database is released to the Public Domain by:

Global Associates, Ltd. Suite 206 1206 Laskin Road Virginia Beach, Va.

Ph. (804) 428-4902

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ALL USERS OF THESE MATERIALS ARE TOTALLY RESPONSIBLE FOR THEIR USE AS THESE MATERIALS ARE PROVIDED WITHOUT EITHER EXPRESS OR IMPLIED WARRANTIES OF ANY KIND. =====================================================================

2. Detail levels

Every map vector has a detail level, range 1 to 5. The closer you zoom on the map, the higher is the detail level. When you see the whole map, only 10% of the vectors are displayed. When you zoom at the maximum zoom factor, 100% of the vectors of the portion of the map are displayed.

3. Projections

Amiglobe displays the map in 4 different projections:

flat or "plate carrée": Coordinates of each point (longitude, latitude) are converted by homothety, in screen coordinates.

Lambert: The latitudes are converted into screen coordinates by calculating the sinus of the angle latitude 0 - Earth's centre - considered point's latitude.

Mercator: The Mercator Map was developed in 1569 by cartographer Gerhard Kremer, whose surname (meaning "merchant" in English) becomes Mercator in Latin. It has since been used sucessfully by sailors to navigate the globe since and is an appropriate map for this purpose.

spherical: The Earth as it would appear from space

You can toggle between these projections by selecting the appropriate in the combo box of the command panel