INTRODUCTION TO MAP READING
Map work or reading therefore, involves the ability to recognize conventional signs on a map and interpret what those signs mean or represent.
A map is a representation of the earth’s surface as it is seen from the above on paper. A large area of land e.g. town, village or even a whole local government area can be represented on one page of a paper. Topographical maps specifically are used in map reading.
Types of Maps: Their Uses
- Maps are classified on the basis of their scales:
(a) Small Scale Maps:
These represent large areas, e.g., maps having scales of 1 cm = 400 km or 1 inch = 50 miles can be considered as small scale maps like wall maps and maps in school atlas.
(b) Large Scale Maps:
These maps represent small areas, e.g., maps with scales lcm=2 metres or 1 inch=1 yard. Town plans, cadastral maps showing boundaries of landed properties etc. are large scale maps.
- Maps classified on the basis of their aims and objectives:
(a) Physical maps show the relief features of the earth with the help of hachures, contours or colour tints between contour lines (e.g. plains in green; plateaus in yellow; mountains in brown; streams/rivers/lakes/seas/other water bodies in blue).
(b) Political maps present a visual picture of the world, or a continent or a country through bold boundary lines or by tints of colours along with boundaries.
(c) Statistical/Distribution maps are related to statistical .data. They may show physical elements like relief, atmospheric temperature, rainfall, air pressure etc.; they may also be used to show social and economic data e.g. agriculture, industry, trade, transport, population, settlements etc.
(d) Topographic maps show physical features of the earth along with cultural aspects like settlements and transportation facilities. Such maps are useful to geographers, military experts etc.
(e) Geological maps show the rock formations, their ages, structures, mineral resources etc. They are prepared on large scales for coal fields, mining areas, engineering, geological features like dams, tunnels etc.
(f) Geomorphological maps show the earth’s physical features, their relationship with land, water etc. on earth’s surface; some conventional pictorial symbols are used to show relief, landforms etc. They are normally on small scale.
(g) Town plan maps show urban landscape on important towns. These are large scale maps.
(h) Cadastral maps are prepared by government agencies for revenue purposes. They show boundaries of landed properties, fields, buildings etc.
(i) Weather maps are prepared by Meteorological Departments showing weather conditions (distribution of atmospheric pressure, wind velocities/ directions, clouds/cloudiness, precipitation etc.).
(j) Bathymetric maps/Navigational maps show the relief of the sea floor/lake floor and are useful for mariners; they also show the nature of the coasts, depth of water etc.
(k) Aeronautical maps show physiographical features of the land, airways, airports etc. for use by pilots.
The various maps mentioned above have the following uses:
(i) Bring out at a glance various geographical elements;
(ii) Bring out the relationships amongst geographical elements;
(iii) For investigation and exploration of resources;
(iv) For planning, optimal utilization and development of resources;
(v) For seeing many dimensions of a region at one time, thus helping in regional planning.
MAP SCALE: The scale of a map indicates the relationship between the distance of two points on a map and the actual or equivalent distance on the ground. In other words, map scale is the ratio, proportion or relationship between measurement on the map and the actual measurement on the ground. Thus, if the scale of a map is 2cm to 1km, it means two centimeters on a map represent one kilometer on the ground.
TYPES OF SCALE
There are three types of scales. These are:
- Linear Scale: This is also known as Graphical Scale or Plain Scale. This is merely a straight line whose length is in certain proportion to the actual length on the ground. This is a special ruler that is drawn below a map that can be used to measure an area or distance. It is divided into a number of equal parts. The divisions on the line scale measures map distances and the labeling will give you the distance on the ground. It is divided into primary and secondary division so that advantages and disadvantages can easily be read from it.
(i) Distances can easily be measured with the help of linear scale.
(ii) If the map is photographically enlarged or reduced, the linear scale is also enlarged or reduced in the same ratio and remains true to the map.
(i) Like statement of scale, this scale can be used by those who are familiar with the unit of measurement used in the scale.
(ii) It requires time and proficiency in drawing a graphic scale.
- Statement Scale: In this method, we express the scale in words, or we make a statement about it; such as one centimetre to one kilometre, or one inch to one metre etc. This indicates that one centimetre on the map represents one kilometre on the ground or one inch on the map represents one mile on the ground.
(i) This is very simple method which is understood even by a common man.
(ii) It requires little time to express this scale.
(iii) It gives correct idea about distance.
(i) It can be understood only by those who are familiar with the unit of measurement used. For example, if we say that the scale of a map is 1 cm : 1 km, it would be understood by only that person who is familiar with the metric system of measurement.
(ii) When a map is reduced or enlarged from the original, the scale does not remain the same. This creates problems in measurement.
The following are features of statement scale;
- The scale are expressed as word statement.
- The scales bear specific units of measurement. The unit of measurement used in the map are smaller than the actual measurements on the ground, for example 1 cm represent 10 km
- The word ”represent” should be used . do not use ”equivalent” or ”equal”. For example, do not say one centimeter in the map is equal to ten kilometers on the ground. This is because the statement is not true. instead say one centimeter on map represent ten kilometers on the ground.
- The map distance always carries the digit 1 while that of the ground may be less than 1 , 1 or more than one.
- A statement scale is simple to express. However it may be difficult for users who are not familiar with the unit of measurement used in the scale. If the map is used or enlarged, the scale will not remain the same.
- Representative Fraction (R. F.): A representative fraction (RF) is the ratio of distance on the map to distance on the ground. Representative fractions are expressed in the form of 1 followed by a : (colon) and then a number, where the one is the numerator in the fraction, the colon represents the division operation, and the other number is the denominator. Thus, a scale of 1:24,000 can be expressed mathematically as 1/24,000. The denominator stands for the number of the SAME UNITS (e.g., centimeters or inches) that the map shows in the real world.
On most maps, the Representative Fraction is given as a ratio, which is usually 1:50,000 on topographic maps. Note that the larger the Representative Fraction denominator, the smaller the scale and the less detail that can be shown. A scale of 1:25 000 will show more detail than a scale of 1:100000. The smaller the denominator of the Representative Fraction, the larger the scale and more detail can be shown for a given area.
Advantages and disadvantages
Representative fractions allow the amount of reduction to be easily understood, but it is harder for most people to determine specific distances on the map because distances must either be multiplied or divided by the RF. Representative fractions are invalid if the map is reduced or enlarged. An advantage of adding RFs to your map is that they are extremely easy to determine in ArcMap – simply look at the Map Scale text on the to bar menu of the ArcMap interface. If you do plan to use an RF and the current scale of your map is a number that is not either standard or rounded off, you should change your map scale before creating the final version of your map so that the RF is an easier number for your map readers to understand. Sometimes it is helpful to provide a scale bar along with the RF to give your map readers the advantages of using both.
Scale Use in Geography:
- Geographic analysis: A scale provides a geographical analysis to a specific surface feature on the map. The analysis explains the significance of the land feature and the distance between landmarks. The geographical analysis confirms the land feature type as a mountain, building, or road.
- Accuracy: A scale presents an exact value of the object illustrated in the map. Accurate landmark information provides landmark facts and figure. Examples are naming a street, building, mountain, or road.
- Geometrical Presentation: Using a geometrical presentation highlights the landmark’s visibility. There are shapes that represent the distance, elevation, and the structure of a landmark. These are sharp-edged shapes that represent buildings and landmarks on the map.
- Time Management: A scale conserves time and effort while studying the map’s land geography. Each scale details the landmarks and geographical distance. Map readers are no longer required to conduct a research to understand landmark geography.
- Introduce the place to visitors: Tourists relies on scale maps to navigate the landmark’s geography. The scale map educates the tourists about the landmark’s name and the distance between land features. As an example, the map illustrates the total distance of the white sand beach, which is 8 kilometers long.
- Education: Scales in map increases anyone’s knowledge about the geographic details of an object, scene, or a geographical position. The scale provides the actual name of the object to prevent confusion. An example is Mount Rainier, which has an elevation of 4,392 meters above sea level.
Disadvantages of Scale:
- Consumes Time: Creating scales in a map consumes time and effort. This process takes at least one month to install scales in a map.
- Requires Thorough Research: A scale needs a reliable information source about the actual name of the landmark. The purpose is to verify the name of the object and the distance between landmarks.
- Need Constant Updates: Scales requires constant updates. Every landmark naturally changes over a time. The environment’s weather and geology gradually changes the physical appearance of a landmark.
- Expensive: Creating a map scale costs a significant amount of money. The equipment and the professional services of scale creators require fees to install a scale on maps. Each scale can cost from hundreds to thousands in USD currency on every map scale.
- Safety concerns: Making a scale map risks the creator’s lives and the health. Creators site visit might be a unsafe. As an example, scale map creators encounters road accidents or injuries while conducting a survey.