Get to Know the Skills and Steps to Read a Map – Map skills and understanding of the compass and how to use it are absolute and need to be learned. What is flat navigation? Navigation is one’s way of determining the direction and position of a trip, either on a map or even on the actual terrain. That’s why navigational knowledge such as maps and compasses and techniques for using them must be understood.
This skill will come in handy in many ways, such as when visiting distant and unfamiliar places. In addition, knowledge of ground navigation is also very much needed in efforts to help victims of natural disasters, someone who gets lost in the mountains, and victims of plane crashes. Another example is for sports purposes such as orienteering competitions.
A topographic map is a two-dimensional depiction (on a flat plane) of the whole or part of the earth’s surface projected with a certain ratio or scale. The longer the map develops, of course, adjusting to its use and needs. Topographic maps come from the Greek “topos” which means place and “graphien” which means to draw, generally these maps are used for land navigation purposes and have a scale of 1:24,000.
In this map, places on the earth’s surface that have an altitude equal to sea level will be depicted in the form of contour lines, one contour line is interpreted to represent one height. Even though topographic maps map each particular elevation interval, various information is still included to help find out more about the area of the earth’s surface referred to on the map. These descriptions are known as map legends.
Map Reading Skills
Apart from being used for military purposes, now maps are also widely used by civilians for fishing, camping, hiking, mountain climbing techniques, walking along roads, or other uses that are directed to a destination or place (navigation). In fact, as much as 80% of the existing work also involves georeferenced data that can be extracted on a map.
1. Read the Contour Lines
There are various functions of topographic maps, for example they are used when making thematic maps such as archaeological maps and tourist maps, and can be used as base maps or base maps (in Prihandito 1989: 17). According to archaeological surveys, topographical maps are very useful for obtaining an overview of an area being studied. For example, when the survey terrain conditions are tough, an existing map can be used to help plot the archaeological findings. This mapping, although only temporary, is very effective for storing and preserving archaeological data (Hascaryo and Sonjaya 2000: 1).
- The ridge of the mountain, is a series of contour lines in the form of the letter U. The end of the letter U indicates a place or area that is shorter than the contour above it.
- Valley or river, is a series of contour lines in the shape of n (the letter V is upside down) and with sharp ends.
- Flat and steep sloping areas, flat or sloping areas are marked with sparse contour lines, while steep or steep areas are marked with dense contour lines.
2. Calculate Contour Interval Prices
An example in calculating contour intervals, on a 1:50,000 scale map, it is found that the contour interval is 25 meters. If you want to reach the contour interval, apply the X scale formula to the map. However, not all maps apply this formula, for example the map on Mount Merapi/1408-244/Jica Tokyo-1977/, the map legend shows that the contour interval is 10 meters, so the formula that applies is X map scale. So, there is no standard formula for calculating contour intervals. However, there are several ways you can do it, which are as follows:
- Find two points of elevation that are different or close together. For example, point B with C, calculate the difference between the heights of the two
- Count the number of contours between A and B
- Divide the height difference between AB by the number of contours between AB and the result is the contour interval.
3. North Map
When viewing a topographic map, the first step to take is to find north of the map. Then look at the map title, usually the map title is always at the north and top of the map. Then look at the writing of the name of the village or mountain on the map column, the north of the map is the top of the writing. There are three directions of north that need to be understood before using a compass and a map, because they don’t line up. The three north directions are:
- True North (True North/US/TN) is given the symbol * (star), namely north through the North Pole in the South of the Earth.
- North of the map (Grid North/UP/GN) is given the symbol GN, namely North which is parallel to the vertical mesh line or Y axis. Only on the map.
- Magnetic North (Magnetic North / UM) is given the symbol T (half of the pariah), namely North which is shown by a compass needle. Magnetic North always changes every year, from west to east or from east to west. This is due to the influence of the earth’s rotation. The three north directions are not on one line, so angular deviations will occur, including:
- The angular deviation between US – UP to both West and East, is called Map Ikhtilaf (IP) or Merimion Convergence. True North (US) will be the benchmark.
- The angular deviation between US – UM both to the West and to the East is called Magnetic Ikhtilaf (IM) or Declination. l True north (IS) will be the benchmark. The deviation between the UP angle and the UM angle will turn eastward or westward, it is referred to as Deviation or Ikhtilaf Utara Peta-North. The benchmark is North Pela f71′) and the corner diagram is drawn.
4. Get to know the Medan Signs
For orientation purposes, landscape forms that are conspicuous in the field must be used so that they are easily recognized on the map, these are referred to as terrain markings and are found in the map legend. There are several terrain signs contained in the beta that can be read before leaving for the field, namely:
- Valley between two peaks
- Steep valley
- Crossroads or the end of the village
- The intersection of the river with the footpath
- Branches and river bends, waterfalls, and others
- For flat areas can be used, crossroads and river forks, bridges and others.
5. Read Coordinates
Reading map coordinates, first understand geographic coordinates. Geographic coordinates themselves generally read map coordinates that are often used in Indonesia. Through these geographic coordinates, it will determine a point by relying on two lines, namely longitude and latitude.
Because it is the foundation for mastering map reading to the fullest. There are two ways to express coordinates, namely Specifying coordinates. This is done on the map and not on the ground. The designation of these coordinates uses:
- Six-digit system, for example: Coordinates of point A (374:622), point B (377:461)
- The Eight Numbers Way, for example: coordinates point A (3740:6225), point B (3376:4614)
- Geographic Coordinate Method, for Indonesia as a benchmark for calculations is Jakarta which is considered 0 or 106° 44′ 27.79″. So that in the territory of Indonesia the initial calculation is the city of Jakarta.
6. Corner Map
The way to calculate the angle of the map is from the north of the map towards the target line and clockwise. In this calculation, the azimuth system (0° – 360°) is used for angle readings. This system is a system that uses horizontal angles whose magnitude can be measured or calculated in a clockwise direction from a fixed line, namely north.
Aims to determine directions on the terrain or on the map and to check the direction of travel, because the line that forms the compass angle is the direction of the path that connects the starting and ending points of the journey. Based on the compass angle, the angle calculation system will be divided into two.
7. Map Arrangement
Map composition is a medium for storing and presenting information about the appearance of the earth by presenting it at a certain scale. To make it easy to search and manage, map indexes are made in graphical or text form. Images of the elements of the earth at a certain scale cannot always be presented according to their size, because they are too small to be depicted.
If these elements are deemed important and need to be presented, then the presentation will use certain image symbols. This is intended to make maps easy to read as well as easy to understand, so various kinds of map information on maps of a certain scale must be described or presented in certain ways.
- Color: used to distinguish various objects, for example roads, rivers, rails and others.
- A list of symbol collections on a map is called a map legend: used to distinguish or further detail the symbol of an object, for example the color of sandstone on a Geological Map is yellow, claystone is green and so on.
- A collection of symbols and notations on a map are usually arranged in a group of map legends which are always presented on each map sheet.
- Elements of a map legend are commonly used to facilitate the reading and interpretation of various maps by various users with various needs.
- A map has high informational value if it contains elements, among which are; map scale, elevation (or contour) information, direction information (usually north of the map), coordinates, legend, map index, as well as other elements deemed necessary.
8. Map coordinates
In the maps that we commonly encounter, we get map coordinate values in several systems such as Bessel coordinates, UTM coordinates and local coordinates. Geological maps or topographic maps that are often used in Indonesia mostly use the UTM coordinate system. However, when taking measurements directly in the field using a measuring device called a theodolite, the coordinates used are local coordinates.
If you want to convert to UTM coordinates from local coordinates, then at the beginning of the measurement, during the polygon creation process, before the step must be linked to a fixed point or benchmark where the position of the UTM coordinates is known. If this has happened, then UTM coordinates can be done.
9. Map Orientation
Map orientation is to equate the map with the actual terrain. Before you start orienting the map, try to get to know the striking signs of the surrounding terrain and their position on the map. The trick is to match the names of rivers, villages, peaks, and so on. So at least you already know where it is. This orientation serves to estimate whether your position is correct.
Try to find a place that has an open view, so that the orientation steps taken on the map show striking signs. First, prepare a map and compass, then place it on a flat surface. Then put the map based on the compass, then the map direction will match the actual terrain.
Look for the most prominent terrain signs around you, and find them on the map. Do this for several terrain marks. remember the markings, their shape and place on the actual terrain.
1o. Triangulation Point
Apart from contour lines, you can also know the height of a place with the help of elevation points, which are called triangulation points, this point is a point or object that is a pillar or milestone. This point will show the absolute height of a place above sea level. Types of triangulation points:
- Primary Point, 1′.14 goal height point. I, No. 14, 3120 meters above sea level. 3120
- Secondary Point, S.45, high point of goal. II, No. 45, 2340 meters above sea level. 2340
- Tertiary point, 7:15 , high point of goal.III No. 15, height 975 meters above sea level 975
- Quarter Point, Q20 , high point.IV No. 20, height 875 masl 875
- Intermediate Point, TP.23 , Antara altitude point, No.23, 670 meters above sea level 670
- Cadastral Point, K.131, Kedaster altitude point, No.I 31, tg 1202 masl 7202
- Quaternary Cadastral Point, KQ 1212, Quaternary Cadastral Point, No. 1212, height 1993 masl 1993
11. Using Maps
In planning a trip using a topographic map, of course the starting point and ending point will be plotted on the map. Before walking note the following:
- Starting point coordinates (A)
- Destination point coordinates (B)
- Map angle between A – B
- What field marks will be found along the A – B track
- How long is the path between A – B and how much – the time it takes. What needs to be considered in carrying out an operation is that we must know the starting point of our departure, both on the ground and on the map.
- Use clear terrain markings both on the terrain and on the map
- Use a compass to see our direction, whether it is in accordance with the terrain marks that we use as a benchmark, or not
- Estimate how far the track will be. For example, 5 km flat terrain takes 60 minutes and climbing terrain takes 10 minutes. Do orientation and resection, if circumstances allow
- Always be alert and also pay attention if there are changes in travel directions and changes in terrain conditions, crossing the end of valleys, crossing rivers and so on.
- The way to make the actual trajectory on the map is to line the road horizontally and vertically, adjusted to the map scale. Then draw the track on the map so that it shows the shape of the map and cross section, as well as the slope of the track. For the length of the track, how to measure it is by using the scale on the map, it will get the actual length of a track.
12. Contour Lines
Contour lines are one of the most important elements in a topographic map, contour lines are information about the height or elevation of a place against its reference. If you want to represent variations in the elevation of a place on a topographic map, the most common way is to use contour lines or contour lines .
Contour lines are lines that serve to connect points with other points that have the same height. The +25 m contour line means that this contour line connects points that have the same height, namely +25 m to a certain height reference.
Formation of contour lines can be done by making a vertical projection of the lines that become the intersection of the horizontal plane with the earth’s surface onto the horizontal plane on the map. Because maps are generally made at a certain scale, the shape of the contour lines will also be reduced according to the scale made for the map.
Map Reading Technique
- Starting point: We must know our starting point, be it in the city or in the field. Note the coordinates if you like plotting the point on the map.
- Terrain Signs: Use clear terrain markings (continuous ridges, streams, cliffs, etc.) as guidelines or directions for travel. The way to recognize it is to interpret the map.
- Compass Direction: Use a compass to see the direction of our journey. Is it in accordance with the direction of the mountains or rivers that we follow.
- Estimating Distance: When walking, always try to estimate the distance and always pay attention to the direction of travel. We can look back and see the amount of time that has been used. Distance is calculated using the map scale, so we get an estimate of the distance on the map. It should be remembered that our estimate is not certain. 10′ x 10′ for maps at a scale of 1:50,000, 20′ x 20′ for maps at a scale of 1:100,000. A map that has a size of 20′ x 20′ is also called LBD, therefore at 20′ on a line along the equator (40.068) is the longest parallel. 40.068km: (360° : 20′) = 40.068 km: (360° : 1/3) = 40.068 km: (360° x 3) 40.068km : 1080 = 37.1 km So 20′ along the equator is 37 .1km. If a distance of 37.1 km is depicted on a 1: 50,000 scale map, it will have a distance of: 37.1 km = 3,710,000 cm. So that on the map: 3,710,000 : 50,000 will have a distance of: 37.1 km = 3,710,000 : 50,000 = 74.2 cm. Consequently 1 LBD map 20′ x 20′ scale 1:50,000 along the equator measuring 74.2 x 74.2 cm. It is impractical to use.
- Map Sheet: Because the LBD is impractical to use, because it’s too wide. Then each LBD is divided into 4 parts with a size of 10′ x 10′ or 37.1 x 37.1 cm each. Each part is called a map sheet or sheet, and is given the letters A, B, C, D. If the scale of the map is 1:50,000, then the map has a size of 50,000 x 37.1 = 1,855,000 cm = 18.5 km .
- The meridian (longitude) that passes through Jakarta is 106° 48′ 27.79″ East is used as the principal meridian for topographic map numbering in Indonesia. Jakarta as longitude 0.
Recommended Books & Articles Regarding Map Reading Skills
Source: from various sources