Using Topographic Maps I
- Published: Sunday, 28 December 2014 11:28
- Written by Lance Hartley
1 - 2 crew
- 1:25000 topographic map
- Bega Map magnetic compass
- The detail in maps is determined by scale and the scale of a map is a ratio of a single unit of distance on a map to equivalent distance on the ground. The map scale is usually located in the legend box of the map which contains explanations for the symbols and other important information.
- A scale expressed as a ratio of say 1:10,000 means that one unit on the map represents 10,000 units on the ground, i.e. 1 centimetre represents 10,000 cm, expressed better as 100 metres. Other good examples are:-
- 1:100,000 map scale - 1 cm = 1 kilometre on the ground (as above)
- 1:250,000 map scale – 1 cm = 2.5 kilometres on the ground
- 1:1,000,000 map scale – 1 cm = 10 kilometres on the ground
Maps with a scale of 1:25,000 or 1:50,000 are termed 'large scale' maps and are best for bushwalkers or hikers as they provide a lot of detail. Maps between 1:50,000 and 1:250,000 are termed 'intermediate scale'.
Latitude and Longitude
- If you look at a map the lines running horizontally depict latitude. Degrees of latitude are number 0 degree to 90 degrees with 0 degrees at the equator, 90 degrees south being the South Pole and 90 degrees north being the North Pole. Longitude lines, also known as meridians, run vertically on a map. Greenwich, England is zero degrees longitude and the degrees continue 180 degree East and 180 degree West until they meet to form the International Date Line.
- Topographic maps depict natural and constructed features on the Earth's surface. For example, landforms which are represented by contours and spot heights, dams, roads, tracks, lakes, indigenous lands, national parks and state forests.
- To understand and interpret topographic maps some study or training is required. Not to oversimplify the detail on the maps, topographic maps depict contour lines to join points of height or equal elevation. Contour lines close together indicate a steep slope, two or more contour lines merging indicate a cliff and distant contours indicate a shallow slope. Contour lines can form 'V' shapes along stream or creek beds or valleys with the V pointing upstream or uphill.
- Topographic maps are of particular use to bushwalkers and government environmental agencies particularly where there is no road or track found on a map to follow. A compass is a 'must have' for such trips.
All mapping and coordinate systems are based on a datum. A datum is a mathematical surface (overlay) that best fits the shape of the earth.
- AGD66 = Australian Geodetic Datum 1966 – Ausraliant region only
- AGD84 = Updated version of AGD66 - used on 2nd edition topographic maps
- GDA94 = Geocentric Datum of Australia
- Adopted because it best fits the earths surface as a whole
- Used on 3rd edition topographic maps
- WGS84 Used for Satellite based navigation.
- WGS84 & GDA94 for practical purposes are the same.
UTM Zones in Australia
Australia is covered by 30 zones in the Universal Transverse Mercator grid system. Each zone is referred to by:
- A number to refer a region of longitude which is 6 degrees "wide",
- A letter to refer to a region of latitude which is 8 degrees "high".