Digital Map of the World
by Peter Loud

Limitations of original data

The Digital Map of the World Series has been developed from the U.S. Government Operational Navigation Charts, and Vector Product Format data. In this data set there are many errors and omissions. It was decided that it was better to minimise modifications to the original data, leaving the developer to work with original U.S. Gov. data. Any errors and omissions in the original VMap data will exist in DMW. The original surveys probably took place over several years and have not been updated therefore roads, urban boundaries and other such features will be outdated to varying degrees. 

The main problems are noted below. 

Non Uniform Map Tiles
The data set is made up of data from a large number of map tiles. These tiles have not all been produced to the same standard, therefore there are inconsistencies in map content and distinct discontinuities at map tile edges. When developing maps from this data there are advantages in checking around the target area and using boundaries corresponding to these original map boundaries. 

Incomplete datasets.
There are many areas thought out the world where the original data is missing. For example, in South Asia, & Australia there are no spot heights between 75° E & 90° E and 106° E & 120°E. In several areas contour lines are missing.

Roads
There are many inconsistencies in classification of roads. This can clearly be seen at the edges of map tiles, particularly in the region of Northeast India, North Burma & South China. In this area some roads were shown in the Roads layer as 'Secondary Road' on one map tile but the continuation of the line did not exist in the Roads layer on the adjacent map tile. On the adjacent map tile the line existed in the 'Trail' layer, classified as a trail. To simplify this, the Trail layer was merged into the Road layer. The original classification and identity codes were retained.

Contour Lines
Originally heights were in feet, but in the VMAP dataset heights have been converted to meters. In DMW the contour line table includes the height in feet in addition to the VMAP meters. In converting the contour line height in meters back to feet it was possible to avoid rounding errors as the original heights were round figures. This was not possible with the heights for Spot Heights and Airport altitude as there would be a double rounding error, therefore these are given in meters only.

There are many inconsistencies in the contour line layer. For most of the map tiles the contours are every 2,000 ft, but in some areas there are contour lines every 500 ft. or every 1,000 ft. This results in many discontinuities at the edges of map tiles. For an example of this check 77°E, 32°N. There are a few contour lines that obviously have the height incorrect. 

There are many areas where contour data is incomplete. There are several such areas in Indonesia, South America and in Nepal.

Contour polygons are not included with VMap or DMW data. They can be created from the contour lines but errors and omissions mean that subjective assessments may be required to complete a polygon.

Water Courses, (Rivers/Streams)
At the edges of the original map tiles there are instances where rivers do not match or may simply stop.

Text Layers.
After conversion of the original data most text layers were displaced from their correct position and the font size extremely large. Initially an attempt was made to re-position the text. However this was not as simple as it appears. Because text could be to the left, right or otherwise of the named feature having the correct font size was essential for the accurate re-positioning. Ultimately it was decided that it was better to leave to text in the original position so that users could re-position the 'raw' data to suit their own requirements.

Marine Features
This group of features has been re-arranged from data originally under other groups. Wrecks & Rocks were taken from the Hydrographgy group and Lighthouses from the Population group, to give marine point features. Sea ice has come from Physiography. Coastline, and sea depth features have come from the Boundary group.

Populated Places
In some areas there were two categories of populated areas, in other areas only one. To standardise and simplify use of these layers/data these populated areas were combined to produce a single category of populated areas. The original classification codes were retained.

Similarly there were, in some areas, two categories of populated point data. These were combined to give only one layer. From this populated places point data Lighthouses were transferred to the Marine point layer.

A significant number of populated places are un-named in the original VMap0 data. The spelling of place names is not always what you expect.

Industry and Utilities
In the original DCW & VMap data Industry & Utilities features were grouped on what were probably military criteria. In DMW these layers have been re-arranged, combining similar features. In all cases the original classification code has been retained. This simplifies use of these layers/data. 

In the original data there were separate groups for Industrial sites and Utility data. These groups have been combined into Industry, (Ind_Utils).

Various Industry and Utility layers with point features have been combined. Similarly, utility lines layers were combined.

Map Layers

These are the standard layers in DMW. Inconsistencies in naming in the original VMap data means that not all DMW datasets use exactly these names. In the conversion to Shapefile format in some instances the original point datasets became both a point and font datasets after conversion depending on the font used.

Transport
	RoadL		Roads				Line
AeroFacP	Airfields 			Point
	RailRdL		Railways			Line
	RRYardP	Railway yards			Point
	TransTrc	Transport feature			Point
	TransTrL	Transport feature			Line
	DQLine		Data Quality			Line
	TransTxt		Transport related text		Point + Text

Population
	PopA		Populated areas/cities		Polygon	
	PopP		Populated place			Point
	PopTxt		Populated related			Point + Text

Boundaries
PolBndA	Political Areas, Countries,	Polygon
PolBndL	Political Boundaries		Line
PolBndP	Political	points			Point
BarrierL		Barriers				Line

Hydrographic
WatrcrsL	Rivers				Line
InwaterA	Inland water			Polygon
MiscL		Misc. water feature		Line
MiscP		Misc. water feature		Point
	AquecanL	Canals				Line
	HydroTxt	Hydro related text		Point + Text

Marine
	CoastL		Coastline			Line
	DepthL		Sea depth			Line
	MarineP		Misc. Marine points		Point
	OceanSea	Oceans & Seas			Polygon
	SeaIceA		Sea Icefields			Polygon

Elevation
	Contourline	Contour lines			Line 
	ElevP		Spot heights			Point

Ind_Utils
	UtilsL		Utilities 			Line
	IndP		Industry				Point
ExtractA	Extraction Inustry		Polygon
	FishIndA	Fishing industry			Polygon
	DQLine		Data Quality			Line
	UtilTxt		Utilities				Point + Text
	IndTxt		Industry text			Point + Text

Physiography
	Grounda		Ground feature			Polygon
	LandIceA	Ice field				Polygon
	LndFrmL	Land feature			Line
	PhysTxt		Physiography			Point + Text

Assorted
	Foreground
	Background

DataQuality
	DQArea
	DQLine

LibRef
	LibRef
	LibRefT

Tile Ref
	TileRef
	TileRefT

NIMA F-Codes

These codes allow the following entities to be selected and manipulated individually.

Hydrography
	Point features
	Spring/Water-hole		BH170
	Rapids				BH120
	Dam/Weir			BI020
	Waterfall			BH180
	Lock				BI030
	Island				BA030
	Rock				BD130
	Wreck				BD180

	Line features	
	River/Stream			BH140
	Inland Water			BH000
	Breakwater/Groyne		BB040
	Seawall				BB230
	Linear Dam/Wier		BI020
	
	Area features
	Inland Water			BH000
	Land Subject to Inundation	BH090

	Text features
	Hyrography Named Location	ZD040
	Hydrography Text Description	ZD045

Elevation
	Point features
	Spot Elevation			CA030
	Inland Water Elevation		CA035

	Line features	
	Contour Line - land		CA010

Industry
	Point features
	Mine/Quarry			AA010
	Well				AA050
	Oil/Gas Field			AA052
	Salt Evaporator			BH155
	Processing Plant/Treatment Plant	AC000
	Oil Gas Facility			AC040
	Tower, non-communication	AL240
	Depot - Storage			AM010
	Tank				AM070
	Water Tower			AM080

	Area features
	Mine/Quarry			AA010
	Oil/Gas Field			AA052
	Salt Evaporator			BH155
	Fish Hatchery/Fish or Marine Farm	BH050

	Text features
	Industry Named Location		ZD040
	Industry	Text Description		ZD045

Boundaries
	Point features
	Administration Area		FA001

	Line features
	Coastline/Shoreline		BA010
	Depth Contour			BE015
	Administrative Boundary		FA000
	Defacto Boundary		FA060
	Armistice Line			FA020
	Cease-Fire Line			FA030
	Claim Line			FA040
	International Date Line		FA110
	Wall				AL260

	Area features
	Administrative Area		FA001
	Water - except Inland		BA040
	Demilitarized Zone		FA070
	Zone of Occupation		FA170

	Text features
	Boundaries named Location	ZD040
	Boundaries Text Description	ZD045

Physiography
	Line features
	Ice Cliff				BJ040
	Bluff/Cliff/Escarpment		DB010

	Area features
	Ground Surface Element		DA010
	Snow/Ice Field			BJ100
	Pack Ice				BJ070

	Text features
	Physiography Named Location	ZD040
	Physiography Text Description	ZD045

Populated Places
	Point Features
	Built-up Area			AL020
	Settlement			AL105
	Native Settlement		AL135
	Camp				AI030
	Building				AL015
	Cairn				AL025
	Monument			AL130
	Ruins				AL200
	Wall				AL260
	Lighthouse			BC050
	Military Base			SU001

	Area features
	Built-up Area			AL020
	Native Settlement		AL135

	Text features
	Population Text Description	ZD045

Transportation
	Point features
	Airport/Airfield			GB005
	Railroad/Marshalling Yard	AN060
	Bridge/Overpass/Viaduct		AQ040
	Ferry Crossing			AQ070
	Tunnel				AQ130
	Causeway			AQ064
	Ford				BH070

	Line features
	Railroad				AN010
	Road				AP030
	Trail				AP050
	Aerial Cableway/Ski Lift Line	AQ010
	Pier/Wharf/Quay			BB190
	Bridge/Overpass/Viaduct		AQ040
	Causeway			AQ064
	Ferry Crossing			AQ070
	Tunnel				AQ130
	Ford				BH070
	
	Text features
	Transportation Named Location	ZD040
	Transportation Text Description	ZD045

Utilities
	Point features
	Power Plant			AD010
	Substation/Transformer Yard	AD030
	Pumping Station			AQ116
	Communication Building		AT050
	Communication Tower		AT080

	Line features
	Pipeline/Pipe			AQ113
	Power Transmission Line		AT030
	Telephone/Telegraph Line		AT060

	Text feature
	Utilities Text Description		ZD045