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NATMAP 2003
information In 2003 two versions of NATMAP Raster were released. The differences are outlined below.
More information on coordinate systems and why the different products are suited to different applications is found in the Coordinate Systems. Why are there are two versions? Two versions of NATMAP Raster were released in 2003 to meet the different needs of digital map users. The main difference is the map projection used for the map images. A map projection is a mathematical formula used to convert a position on the earth (a latitude and longitude) to a coordinate on a flat piece of paper. A map projection is not perfect however (think of trying to flatten an orange peel – you can’t do it without tearing or stretching part of the peel). The area, shape or distance between points on the earth will become distorted depending upon the type of map projection used. Depending on what you want to use the map for, you can stop distortion for one or some of these properties, but not all. The Mosaic uses what is known as an Equirectangular map projection. This assumes that one degree of latitude equals one degree of longitude, and uses degrees as the unit of measurement. This is the simplest map projection, and it’s great for using with GPS or computer mapping because it doesn’t need complicated maths to convert positions. You can also easily create one big map of Australia. However, in reality one degree of latitude does not equal one degree of longitude. This is because latitude is pretty much constant all over the earth, but lines of longitude meet at the poles, meaning they get closer as they near the North or South Pole. Around Darwin, one degree of longitude is about 106 kilometres; around Hobart, one degree of longitude is about 79 kilometres. This also means that map scale varies depending on where you are, and the shape of the southern parts of Australia becomes very stretched and squashed.
Mapsheets uses a map projection called the Map Grid of Australia (MGA), which is basedon an international map projection called UTM. The world is divided into zones, and in each zone you can measure distances accurately and the shapes of features are preserved. As this map projection uses metres rather than degrees, map scale is constant. Therefore these maps are best if you want to measure distances, especially from a print-out. The disadvantages of this map projection are that the map projection formula is complicated (although you can still use these maps with GPS), and you can’t measure distances accurately beyond about 80km into the next zone. Whilst you could join maps within the same zone, you can’t join maps across zones because of this distortion. Because you can’t join maps together easily, the maps in Mapsheets remain as individual map images. Whilst you still need to load each map individually, it does make it easier to store maps in different places (such as on your hard drive) to improve performance. Updated features for 2003
Features retained in 2003 from 2002
All other components in the two products are the same as in previous versions. Are upgrades available?At this stage no - if you want updated maps and/or Viewing software, you need to buy the new version. Copy of on-line help file is here. --------------------------------------------------------------------------------A list of map/sheets and their changes from Version 3 to Version 2003
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