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TOPOCADASTRAL AND ATLAS MAPS

Objectives: By the end of this subtopic learners should be able to:
  • Classify and interpret symbols on a map.
  • Describe the importance of a key.
  • Identify and use the different types of scale.
  • Use coordinates to locate places on a map.
  • Measure distances accurately on a map.
  • Calculate direction and bearing on a map.
  • Draw and interpret sketch maps.
  • Recognize various features represented by contour lines on maps.

A Map

Definition Of Map:

  • A map is a representation of physical and human features of an area of the earth’s surface drawn to scale on a flat plane or piece of paper.
  • Features represented on a map are both natural (relief, water, vegetation) and man-made (buildings, roads and other landuse)

Topocadastral Maps

  • A topographical map is a map that shows relief, water and vegetation features of an area.
  • Topocadastral maps are maps that show both topographical features of an area as well as additional information such as farm boundaries.
  • The main type of map used in Zimbabwe’s school system is the 1:50000 topocadastral or topographic map.

Atlas

  • This is a book of maps.
  • It contains many types of maps presented in different scales.

Map symbols and references

Symbols

  • Maps, unlike photographs, use symbols to represent actual features.
  • These symbols are generally agreed by cartographers (map makers).
  • Map symbols are classified into two groups: those representing physical features and those representing human features.

Symbols of physical features

  • Symbols of physical features are further subdivided into water, relief and vegetation.

Water features

  • All water features are represented on a map with the associative colour blue.
  • The water features may be natural such as streams, springs and marsh or manmade such as dams, water tanks and canals.
  • In the presentation of symbols below water features are shown in their colour blue.
Water Features
  • Although not all of the water features may be memorised, it is important to keep familiarity with the following: small stream, river, waterfall, rapid, well, borehole, dam, reservoir and marsh.

TASK:

Identify from the key given below and reproduce, by drawing, the above named water features in your exercise books.

KEY


  • These are represented in brown.
  • The simplest brown line is a contour.
  • The various contour patterns tell us which feature there is on the map and this requires some set of map reading skills.
  • Contour patterns are discussed further later on in this section of map skills.
  • In the key given below there are a number of relief features that can be found on a topographical map.

Relief Features

  • These are represented in brown
  • The simplest brown line is a contour.
  • The various contour patterns tell us which feature there is on the map and this requires some set of map reading skills.
  • In the key given above there are a number of relief features that need to be read carefully.
  • These can be further compared to another set of symbols given below.

  • Vegetation Features

  • Vegetation features are represented in green colour.
  • The green colour can be of different hue to denote differences in density.
  • In Zimbabwe, we usually use four broad classifications namely: dense bush, medium bush, sparse bush or open grassland and plantation or orchard.
  • In the key below are some vegetation features symbols.


Human Features

  • These are physical features built by humans and they constitute the broadest class.
  • They are mostly represented in black although a variety of other colours may be used to give prominence to some phenomenon.
  • Red is usually used to represent roads and boundaries.
  • The main key given earlier shows the different classes of human features symbols.
  • One can compare those to the small extract given below.

    near Features


Buildings and related features



    The Key

    • The internationally agreed map symbols only provide a guide but more representation of features goes into map making.
    • A key is thus important.
    • It is a guide to symbols used on a map.
    • A key is usually placed in a corner outside the map.
    • The key must contain symbols that clearly resemble those used inside the map in terms of basic shape/character and colour.
    • The word ‘key’ must be clearly labeled on top.
    • Every map must have an accompanying key.

    Location on maps

    Longitude and latitude
    • Location on maps is done using different means that include use of grid reference, direction and bearing.
    • Longitudes are a set of imaginary lines drawn on the earth’s surface for the purposes of locating places.
    • They run from the North Pole to the South Pole.
    • Longitudes are used together with latitudes which are lines drawn parallel to the Equator.
    • Longitude is the angular distance of a place on the earth’s surface to the Greenwich meridian also known as prime meridian (see globe below).
    • Location of places is thus made with reference to either longitude or latitude as is indicated on the globe above.
    • In locating a place we quote the longitude immediately on the left or west and then latitude immediately below.
    • Further insight into location and time zones using longitudes and latitudes is tackled under transport studies.



    Grid reference

    Grid referencing
    • This is a system that uses vertical and horizontal lines on maps.
    • These lines are imaginary and do not have any relationship with features on the map and neither do they have anything to do with longitudes and latitudes.
    • Horizontal lines are called northings and they count from bottom to the top (for example 46 to 49 on the map extract below).
    • They count towards the north of the map and for that reason they are referred to as northings.
    • Vertical lines are called eastings and they count from the left of the page to the right or east (for example 28 to 31 below).
    • Grid referencing is done using four figure and six figure techniques.



    Four figure grid reference

    • We indicate Easting (immediately to the left in the box where the feature is) first then Northing (immediately below).
    • Four figure grid of A is Easting 28 and Northing 48 giving 2848.
    • For B it is 2947 and C 3048.

    Six figure grid reference

    • On the six figure grid system we quote Easting immediately to the left on a scale of one to ten towards the next easting to the right and northing immediately below and its distance towards the next northing above.
    • ‘A’ is thus on Easting 285 and northing 485.
    • Six figure grid reference of A is 285485.
    • ‘B’ is 291473 and ‘C’ is 307487.
    • One very important skill in determining exact position is that of estimating correctly distances on a scale of one to ten.

    Direction

    Compass points

    • Using cardinal and intercardinal points, general location of features can be made on a map.
    • Intercardinal or ordinal points are the eight or sixteen compass points as given below.


    • When telling the direction of one place from the other e.g. A from B, we start at B as shown in the diagram below.
A from B



    • We draw a north-south line at B and connect B to A with a line.
    • We are thus able to estimate the direction of A as south east.
    • Compass points are good in that they are easy and fast to use since they do not entail measurement.
    • They also use the skill of generalization.
    • On a map, the method is most useful in describing location of expansive areas.
    • Its weakness is in the fact that exactness or pin point accuracy of a location is difficult to arrive at.
    • It is not very useful in locating points.
    • Using the sketch map below, direction is useful in locating the school and home which do not happen to be points.
    • The school is in the north-west (NW) while the home is in the south-east (SE) of the map.
    • Accuracy is, however, demanded in locating points A and B on the map in general as well as in relation to each other.
Sketch Map



    • Using bearing is the other way of enhancing use of compass points when locating places.

    Bearing

    • Measurement of bearing is a skill that is extensively covered in mathematics.
    • It involves the use of both compass points and angles.
    • Bearing gives location of a place in relation to another place.
    • An example is the location of B from the position of A.

     


    • Telling the bearing of B from A involves drawing a north south line at A.
    • We draw a straight line from A to B.
    • The bearing of B from A is the angle of B on the north-south line from A.
    • Please note that in this case we use the Grid North.
    • We then measure the angle between the north-south line and the line joining A to B using a compass.
    • Bearing is thus 245°.
    • If we want the bearing of A from B, again we measure from B the angle of A on the north-south line which is 065°.
    • Below is an example of the different angles that can be measured to give bearing of a place.



    • Please note that in all cases the grid north is the one used.
    • Bearing can be given as combination of both compass direction and angle.
    • In the diagram below A is from the north 60° towards the east (N60°E).
    • C is from the south 55° towards the west (S55°W).



    Reverse or back bearing

    • If we move from one point to another we are able to calculate bearing.
    • However, if we return to where we came from we are using reverse bearing.
    • It is reverse because we make a 180° turn to get back to where we were.
    • Reverse bearing is derived by adding 180° to our initial bearing if it is below 180° or subtracting 180° if it is above 180°.
reverse

    • In the above illustration bearing of school from home is 40°. Reverse bearing is thus 40° + 180° = 220°.
    • If our initial bearing from a place is 260° then our reverse bearing will be 260° – 180° = 80°.
    • In the second case, our initial bearing is above 180° so we subtract 180°.
    • Using distance, direction and/or bearing we are able to follow description of routes on maps.



    Scale

    • A map represents the earth’s surface on a piece of paper.
    • This means that the distance on a map only represents the actual distance on the ground.
    • Scale is the ratio of distance on a map to the actual distance on the ground.
    • Scale is the extent to which the actual distance has been reduced so that it is represented on a map.

    Types of scale

    • There are three types of scale: statement, representative fraction/ratio and linear scale.
      1. Statement
        • This is in the form of a descriptive statement such as “one centimeter represents half a kilometer” or “1 centimeter represents 50 000 centimeters.”
      2. Representative fraction or ratio
        • It comes as a fraction or ratio such as 1/50000 or 1:50 000.
      3. Linear
        • Scale is shown as a line with the first part divided into ten units (extension scale) and the second (primary scale) which if you measure with a ruler will show that 1 cm represents half a kilometer.


    Small scale and large scale maps

    • The scale of a map is given by the size of the fraction.
    • When we say 125 000 map is bigger than 1:50 000 map, it is because the fraction 1⁄(25 000) has greater value than
      1⁄(50 000).
    • Most students confuse higher denominator with higher value.
    • The higher the denominator the smaller the fraction and therefore the smaller the map.
    • A small scale map is a map that has a fraction smaller than 1:50 000, for example 1:100 000.
    • Medium scale maps are between 1:50 000 and 1:25 000.
    • Large scale maps are those with scales larger than 1:25 000 such as 1:10 000.
    • Zimbabwean school system normally uses the 1:50 000 topographic map.

    Measuring distance

    • We measure straight lines with a ruler. We divide our measured distances (cm) with our representative fraction (e.g. 1:50000).
    • If we measure distance of 16cm on a map, actual distance on the ground will be:16 / (150 000)= 32km.
    • The challenge of measuring distances on a map comes when we measure curved distances.
    • One simple way is to use a string to follow through all bends and then straighten it up on a ruler to get straight line distance.
    • This is shown in the picture below:

    • Another method is that of using a piece of paper.
    • The paper is turned around as markings are done on all straight distances on both the paper and the map until the whole length that is measured is covered.
    • The markings on the piece of paper are then put against a ruler to measure straight line distance.


    Gradient

    • It is generally described as the degree of slope.
    • It is the relationship between horizontal (run) and vertical (rise/fall) distance.


    • If we look at a simple diagram like one below gradient is given by yx


    • If we regard boxes in the graph as centimeters then it will be35= 0.6
    • What it means is that the ground rises by 0.6 cm per every horizontal distance of 1cm.
    • When this is applied to a map, horizontal distance is straight line distance between two points which can be measured with a ruler.
    • Vertical distance or height is calculated by finding difference in height between contours.


    • Using diagram above horizontal distance is from V to W = 3km.
    • Vertical distance is the difference between contours which is 859m-680m = 179m.
    • Next step is to convert both distances into similar units.
    • Height = 179m and horizontal distance =3000m.
    • Gradient is thus 1793000= 0.05966 = 59.67m/km.
    • For every kilometer there is a rise in the ground of 59.67 meters.

    Estimating area on a map

    • Area is generally calculated by multiplying length by width.
    • However, this may be very taxing given irregular dimensions of most areal aspects of a map such as farmland, cultivated area, a game park, dam and so on.
    • A method of estimation is thus used.
    • Grid lines provide squares of 2cm by 2cm on a topocadastral map of 1:50 000.
    • Because 2cm represent 1 km, it means a box represents 1km².
    • Total area will thus be the sum of full boxes plus all estimate parts.
    • The illustration below gives us total area of 84km².


    Contour lines

    • These are lines drawn on a map joining places of the same height above sea level.
    • Contour lines do not cross.
    • They may come close to each other or even merge where slopes are very steep like on cliffs.
    • The difference between two successive contour lines is called contour interval (CI).
    • On the topographical 1:50 000 map mostly used in schools in Zimbabwe the contour interval is 20m.
    • Labelling of contours is done on the contour lines themselves and in most cases every fifth contour that is bold has the label.
    • The labelled contour such as the 1000m one on the map below is known as an index contour.
    • Contour lines are brown in colour.


    Advantages of using contour lines

    • Contour lines do not obscure any other detail on the map.
    • They are the most effective method of representing features, steepness or gentleness of the land.
    • Can be used together with spot heights, benchmarks and trigonometrical beacons where exact /specific heights are needed.
    • Can be used with layer colouring to classify or distinguish heights.

    Spot height

    • These are dots on a map that mark specific height of a spot.
    • They only exist on maps and not physically on land.

    Trigonometrical beacon

    • These are stations marked on a map as well as on the ground.
    • They indicate the highest point in an area.
    • On the map they are presented in the form of a small triangle that has a specified height beside them.
    • They can, however, be numbered, for example 1200T.


    Benchmarks

    • A benchmark is normally a metal plug that is cast in concrete on the ground and has height engraved on it.



    Contour lines, slopes and common landforms

    • Patterns of contours indicate the types of landscapes.
    • When contours are far apart land is gentle and when they are close together slopes are steep.


    Gentle slope
    • The first contour diagram shows gentle slope while the second shows steep slope.

    Steep slope 
    • A map that has mostly even ground is seen by its sparse contours while hilly areas have predominantly close contours.

    Even slope

    • Slopes are even when contours are evenly spaced and this is common with gentle slopes.
    • The illustration below shows an even contour pattern. 




    Undulating slope

    • A series of gentle up and down slopes give us an undulating landscape or slope.
    • The photograph and map below shows one such landscape.





    Convex slopes

    • These are slopes that are gentle towards the top but steeper towards the bottom.
    • Contours start off far apart at the top becoming closer to each other towards the bottom as shown in the illustration below.



    Concave slopes

    • Concave slopes are slopes that are steep at the top becoming gentle towards the bottom.
    • Contours are therefore close towards the summit but far apart at the bottom or base.



    A Ridge

    • A ridge is an extended highland or mountain with a narrow top.
    • In Zimbabwe ridges are common along The Great Dyke and Eastern Highlands.
    • Below is a picture showing a ridge and its contour mapping.


    Plateau

    • It is also spelt as plateaux.
    • A plateau is a highland or mountain with a flat top.
    • A world example is found in South Africa named The Table Mountain.


    Conical hill

    • This is simply a round shaped hill.
    • The illustrations below show the side view as well as contour pattern.


    Escarpment

    • An escarpment is a sudden fall of land caused by erosion or vertical movement of the earth’s crust.
    • In Zimbabwe we have the Zambezi escarpment in north eastern parts of the country.

    A Valley

    • A valley is an elongated lowland between highlands whose bottom is indicated by V or U shaped contours.
    • The formation of the V and U shaped valleys is extensively covered under rivers features.


    Valley and spur

    • A spur is a highland jutting into a lowland or valley.
    • Spurs are often found interceded by narrow valleys as shown in the diagram below.

    Gorge

    • This is a narrow river valley with deep but steep sides.
    • At Victoria Falls we have the famous Devils’ gorge.
    • More discussion of it is done under landform studies.

    Sketch map

    • A sketch map is a map drawn from observation showing outline of features on the main map.
    • There are no actual measurements and concentration is given to the aspects that need to be mapped ignoring other not so important ones.

    Drawing a sketch map

    • Obtain a base map.
    • Draw a frame of half the scale (1:100 000).
    • Draw the features that you want to focus on, for example, rivers, hilly areas, fields, grasslands and so on
    • Start with rivers, then hilly areas and lastly man-made features.
    • Shading is used to indicate areas while other features may be represented by simple illustrations (for example roads and rivers).
    • Include a title and key or legend.
    • Indicate the grid north.
    • The steps are summarized below on a checklist of sketch map drawing.

    Checklist fo sketch map drawing
    Checlist of sketch map drawing
    • Drawing of sketch maps is a skill that is best mastered by constant practice.
    • The following is an example of a sketch map.


    An example of a sketch mapS