Grid References Many maps are provided with the standard grid overlaying them. This provides a simple and accurate method for finding features on the map. It is a network of intersecting parallel lines - one set is horizontal and the other vertical. The Universal Grid Reference System (UTM Grid) covers the entire world between 84ºN and 80ºS. The grids are 6º wide and 8º deep. The columns are numbered 1-60 starting from the 180º meridian and moving easterly. The rows are identified starting from the south to north and are identified by letters starting at C and going to X (the letters I and O are omitted). Grid sections are identified with the column number followed by the row letter. Hence the grid which covers Newcastle is H56 and the one that covers Shark Bay in WA is 49J. 56H Figure 2.10 The UTM Grid Referenc e System (from Australia n Army Warfare Manual) Each of the grid zones is further divided into 100000m squares. These are identified by combining two additional letters derived through a sequential lettering system. So a full map reference for a point near Newcastle would be 56 H MJ 443868. This is derived from: 56 is the zone number H is the division based on the 8º of latitude MJ is the 100000 meter square definition 443 is 44300 meters 868 is 86800 meters This system allows definition of points on the Earth s surface to within 100 meters. Page 20
Figure 2.11 The UTM Grid Reference System 100000 m square (from Australian Army Warfare Manual) When drawn on the map the horizontal lines are called northings and the vertical lines are called eastings. Eastings are numbered from west to east (left to right). In the example given below note that easting 04 is further east than easting 02. Northings are numbered from south to north. In the example below, northing 03 is further north than northing 01. Places and features on a map can be easily located by referring to the grid on the map. The grid reference usually consists of six figures, for example 010020. The first three figures (010) refer to the eastings whilst the last three figures (020) refer to the northings. Figure 2.12 below shows how the grid reference is made up. Page 21
A is exactly on easting 01, so it's eastings reference is 010. Figure 2.12 Recording fine grid references A is exactly on northing 02, so it's northing reference is 020. One thing to know when giving Grid references is that easting is always given before northing. An easy memory key to remind you of this is that E comes before N in the alphabet. How do we cope if the point we are trying to locate is not exactly on grid lines? The answer is that in these instances the grid square axes are divided up into tenths. In the example given below point C lies 8/10 along from the easting 03 so the easting reference is given as 038. Note that you still count from west to east (left to right). Therefore the grid reference is 010020, or as it is more commonly represented. 010 020 Easting Northing Page 22
Test Your Knowledge Use the grid references below to complete the table. 05 A C 04 E B 03 D 02 01 F 00 G 00 01 02 03 04 05 Letter Grid Ref. A B C D E F G There are times when it is not necessary to give precise positions for features on grid maps. An example of this may be when you have to designate the position of a large feature such as a lake. Obviously no one point will accurately depict its position. In these cases four-figure grid references may be used rather than the normal six-figure. A four-figure area reference refers to a complete grid square, not just one particular point within the square. Page 23
Mapping the Shape of the Land Topographic maps give information relating to their relief, or shape, of the land. In other words they tell us weather of the land is flat or mountainous, and where there are ravines or cliffs. We can easily represent roads, houses and other man-made features on maps using symbols, but hills, valleys and plains are not so easily represented. In order to represent physical features on flat surfaces map makers use several methods to indicate the relief of the land: spot heights contour lines layer shading relief shading. Spot Heights Spot heights are marked on maps using a black dot or triangle with the height written next to it. They give exact altitude above sea level for one particular place. Normally they indicate the tops of hills or mountains, but give no other real information about the shape of the land. Contour lines Contour lines are a method of depicting the 3-dimensional character of the terrain on a 2- dimensional map. Just like isobars in the atmosphere depict lines of equal atmospheric pressure, contour lines drawn on the map represent equal points of height above sea level. Figure 2.13 demonstrates this principle Figure 2.13 Using contour lines to demonstrate height on a 2D Map (from Codrington & Crittenden) Look at the three-dimensional drawing of the mountain below. Imagine that it is an island at low tide. Draw a line all around the island at the low tide level. Three hours later, as the tide has risen, draw another line at the water level and again three hours later. You will have created three contour lines each with a different height above sea level. As you Page 24
see in Figure 2.14, the three dimensional shape of the mountain is mapped by calculating lines of equal elevation all around the mountain, and then transferring these lines onto the map. On multi-colored maps, contour lines are generally represented in brown. The map legend will indicate the contour interval the distance in meters (or feet for US and British Maps) between each contour line. There will be heavier contour lines every 4th or 5th contour line that are labeled with the height above sea level. Figure 2.15 illustrates how a variety of surface features can be identified from contour lines. Figure 2.14 Relationship of contours to height (from www.princeton.edu guide to Map and Compass) Interpreting Contour Lines When using topographic maps you must be able to recognise how contour lines relate to natural features. Figure 2.15 shows a typical contour map and the natural features that it represents. You should note the following points by studying the contours and the picture of the landform together. Steep slopes - contours are closely spaced Gentle slopes - contours are less closely spaced Valleys - contours form a V-shape pointing up the hill - these V's are always an indication of a drainage path which could also be a stream or river. Ridges - contours form a V-shape pointing down the hill Summits - contours forming circles Depressions - are indicated by circular contour with lines radiating to the center Page 25
Figure 2.15 Comparison of contours to features (from www.princeton.edu guide to Map and Compass) Page 26
Test Your Knowledge Use the diagram below and match the correct relief model with the corresponding contour map (from Codrington) Current Australian maps use a contour interval of 40m, with index contours appearing every 200m. Contours are printed in brown. In areas where there are hollows or depressions, depression contours are used. These have small strokes on either side of the contour line which indicates the contours go down not up. Page 27
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Measuring Distances There are a number of ways to measure distance accurately on a map. The simplest is to use a ruler and measure off the scale. This only works well on straight paths, and relies on you having some form of ruler. Another is to use a piece of string or flexible wire to trace the intended route. After tracing out your route, pull the string straight and measure it against the scale line in the map legend. Yet another method is to use a drawing compass (the mathematical kind not a navigational compass) set to a narrow distance on the map scale like ½ kilometer and then "walk off" your route. It is a good idea to be conservative and add 5-10% of the total distance to take into account things like switchbacks that don't appear on the map. It's better to anticipate a longer route than a shorter one. Be wary about estimating distances on a as the crow flies basis as you may seriously underestimate the distance by not allowing for twists and turns in your path. Street Maps and Street Directories For most of you using a street directory is very plain sailing, but just in case you haven t used one we will very quickly cover the basics here. You will find a great deal of information in the street directory as well as street locations. They typically show important public buildings, phones, sporting ovals and also some geographical features such as creeks, rivers lakes etc. How do you use one? The first place to look in a street directory is the index. Generally you will be looking for a street or place, and these will be listed in alphabetical order. A typical index is shown below. Map Number Map Co-ordinates If you wish to find say Meadowbank Crescent on the street map you would look it up in the index and it would say that it is located on Map 54 co-ordinate location J6. Page 29
Maps are located in numerical order so it should be s simple matter of moving through the directory till you reach the correct map. Once here you use the co-ordinates as shown below to located the feature of interest. The item of interest should lie in the region where the two lines from the letter and the number of the coordinates cross. Page 30
Practical Exercise 1 Topographic Maps Part 1 - Scales and Measurement Using Map 1 (Bega Valley) calculate the following and fill in the answers in the table provided: Task 1. The distance from Tathra Headland to North Bega Sports ground as the crow flies Answer 2. The distance from Tathra Headland to North Bega Sports ground via the main road. 3. The approximate walking distance from Kaininny Bay to Bournda Island 4. The approximate time that it takes to walk from Horse Shoe Lagoon in a south east direction to Turingal Head along the walking trail (given that the average walking speed is 4km/hour) 5. The distance by road from Vikings Rest to Horse Shoe Lagoon Page 31
Part 2 Topography Using Map 1 (Bega Valley) provide answers in the table provided: Task 1. When traveling from Bega to Tathra does the road follow a valley or a ridge? Answer 2. Find the vehicular track which leaves the road at GRID REF (GR) 569412 and state whether the track follows ridges or valleys. 3. Which hill is higher, that at GR 584362, or that at 504383. 4. Which Grid Squares have steeper slopes, that at 5940 or that at 5933? 5. How many contour lines are there in area reference 5634? What does this convey about the topography of the area? 6. If you stand in the Bega Valley and look toward grid reference 596388, would you be able to see the town of Bega? Explain. 7. If you stood at GR 523408, would you be able to see the ocean? Part 3 Grid References Using Map 1 provide answers in the table provided: Task 1. Give the four figure area references for Tathra Township Blackfellows Lagoon Turingal Head Betunga Swamp 2. Give 6 figure grid references to describe: Tathra Wharf Bournda Island Frog s Hollow Bridge Wallagroot Lake Boat ramp Answer Page 32
Using Map 2 (Port Moresby) provide the likely job of a person who works at the following places (GR). GR 172590 228696 237559 216731 165524 245650 180638 238627 175601 211572 Answer Page 33