Chapter 1: Interpretation of Topographical Maps
A message reaches a district control room late in the evening. A settlement has been cut off, a stretch of road has slipped away, and a repair party must leave before morning. The caller describes the place the way people always describe places — past the sugar mill, over the bridge, left where the road bends sharply. On the ground, in daylight, that description works well enough. On a dark night, to a driver who has never been there, it is close to useless. Two bridges, three bends, and the party ends up somewhere else entirely. The officer on duty does something different. She opens a topographical sheet of that area, drawn at a scale of 1:50,000, and reads across the numbered lines running up the sheet and then up the numbered lines running across it. She writes down six digits and reads them out. The driver, holding a copy of the same sheet, finds the same square, divides it by eye, and puts his finger on a patch of ground about a hundred metres across. Nobody has described anything at all. Two people, in two different places, are now looking at the same point on the earth.
Diagram
Fig. 1.A1 Caption: The same place can be described in words or fixed by a number, and only one of the two travels. Brief: Two panels side by side — left, a rough sketch with a mill, a bridge and a bending road labelled in words; right, the same area as a gridded sheet with numbered lines and a single square picked out; an arrow from left to right labelled ‘from description to reference’.
1.1 Maps And Their Significance
The earth is a huge planet, and its surface is anything but uniform. It carries relief features of every kind — mountains, plateaus, valleys, rivers, lakes, seas and oceans. Because the earth is so large, and because it is spherical, no one standing anywhere on it can view the entire earth at the same time.
That creates a practical problem. If the whole surface cannot be seen at once, it also cannot be represented on a flat surface as it really is. The difficulty has been resolved by using models of the earth instead of the earth itself, and there are two such models in common use — the globe and the map.
A globe is a three-dimensional representation of the earth. It is the only true representation we have, because it keeps the earth’s own shape, and so it indicates shape, direction, area and other features correctly. Anything you measure on a globe is in the same proportion as it is on the earth.
The globe’s weakness is space. Its surface is small, so it cannot represent physical features and other characteristics in detail, while topographic details — the fine detail of a small stretch of ground — cannot be shown on it at all. The two models therefore do different jobs: the globe is true but general, and a map gives up the true shape in order to show a part of the earth closely.
From A Curved Earth To A Flat Sheet
To draw three-dimensional features like mountains, valleys and rivers, and other geographical phenomena, special techniques are used so that these features can be drawn on a uniform basis. This art and science of mapping is called cartography.
A map is a representation of the earth’s surface, or of a part of it, showing natural or man-made features, drawn to scale on a flat surface. Drawn to scale means every distance on the sheet has been reduced in the same fixed proportion, so distances on it stay comparable with distances on the ground.
Fig. 1.A2 sets the two models side by side, and shows what each one can and cannot carry.
Diagram
Fig. 1.A2 Caption: The globe keeps the earth’s true shape; the map gives that up in return for detail over a small area. Brief: Left, a globe with continents and lines of latitude and longitude, labelled ‘shape, direction and area true — no fine detail’; right, a flat sheet covering one small area with rivers, roads and settlements, labelled ‘part of the surface, drawn to scale, detail visible’.
What A Map Lets Us Study
This description of the earth’s surface helps us to understand various types of phenomena, such as soil, climate, vegetation, rivers, mountains, volcanic eruptions and earthquakes. More than that, it lets us see their inter-relationships — how the soil of an area sits with its rainfall, or how its rivers sit with its relief. Two features drawn on the same sheet can be compared; the same two features described in words cannot.
With the advancement of cartographic techniques, maps have become more accurate, and they give precise and greater details than they once did.
1.2 Elements Of A Map
A map is not simply a picture of the ground. It is a drawing built to a set of rules, and a reader who knows those rules can take information off it that was never written in words. Six basic elements make that possible, and every properly drawn map carries all six.
The six elements of a map are as follows. (a) The title indicates the subject of the map, telling you what has been mapped — the distribution of natural vegetation, water bodies, climate, and so on. Without it you can see the pattern but not know what the pattern is of. (b) The scale denotes the relationship between map distances and actual ground distances. It is what allows a distance measured on the sheet to be turned into a real distance on the earth. (c) Direction refers to the cardinal directions, that is, North, South, East and West. Conventionally a map is aligned with the North towards the top, so unless the sheet tells you otherwise, up the page is north. (d) The grid system is a network of lines that help in pinpointing the location of a place on a map. Usually a grid is formed by lines of latitude and longitude, the imaginary lines you have used since the middle school atlas to fix a position on the earth. (e) Conventional signs or symbols are the graphic language of a map. They are used to represent different objects such as roads, railways, rivers, canals, mountains and oceans, and they carry information that would need a paragraph if it were written out. (f) The key, also called the legend, explains the meaning of the symbols that are used in the map. It is the sheet’s own dictionary, and nothing on the map can be read confidently without it.
Fig. 1.A3 shows where each of the six sits on a sheet.
Diagram
Fig. 1.A3 Caption: Every element has its usual place on the sheet, and a reader learns to look for each one. Brief: A specimen map sheet with six labelled call-outs — title at the top, scale and key at the bottom margin, north arrow at a corner, numbered grid lines along the edges, and two or three conventional symbols picked out within the mapped area.
Where The Symbols Came From
The symbols on a map were not invented all at once. They refer to a graphic language that has evolved through centuries of research and use. They had their origin as simple pictograms, and these gradually developed into the conventions now generally used, which is why the same symbol means the same thing on sheet after sheet.
1.3 Types Of Maps
Maps are not all made for the same job, and they are classified in two different ways. The first way looks at size, that is, at how much ground the sheet covers and how much it has been reduced. On the basis of their size, maps can be classified as large scale maps and small scale maps.
The difference between the two is a trade. A large scale map covers a small area and reduces it only a little, so it has room for detail, while a small scale map covers a large area and reduces it heavily, so the detail has to be dropped. Neither is better than the other; each answers a different question.
1.3.1 Large Scale Maps
Topographical Maps
Topographical maps are prepared after a careful and accurate survey of the area, so what is drawn on them has been measured on the ground rather than sketched. In India, these maps are prepared by the Survey of India, the country’s official mapping agency. They are drawn on scales of 1:50,000 and 1:25,000, which means one unit on the sheet stands for 50,000 or 25,000 of the same units on the ground.
These maps are multi-purpose, and they show natural features such as hills and rivers as well as man-made features such as railways, buildings and canals. Because both kinds of feature appear on the same sheet, the maps are very useful for planning, defence and tourism. Details about these maps are given later in this chapter.
Cadastral Maps
Cadastral maps provide complete details of an area, such as the boundaries of properties and individual buildings. They are used to demarcate the boundaries of fields and buildings in order to register the ownership of landed property, so the line drawn on the sheet is the line that decides whose land ends where.
These maps are maintained by the government for public record. They are used in administration and the realisation of taxes, in the management of estates, and in the identification of property in legal documents. Revenue maps, settlement maps, village maps and city plan maps are all examples of cadastral maps.
1.3.2 Small Scale Maps
Wall Maps
Wall maps are meant to represent large areas that could be viewed at a glance. They show features such as railways, roads, physical and political detail, relief, temperature, population, industries and vegetation. They are used for display purposes in classrooms and museums, where a whole region has to be visible to a room full of people at once.
Atlas Maps
Atlas maps are drawn on a smaller scale still, and are used to represent a whole country on a single sheet. Since these maps are drawn on a smaller scale, they give a condensed and generalised picture of different areas of the world.
The features generally shown by atlas maps include relief, drainage, vegetation, soils, crops, minerals, industries, population and cities. Despite their lack of details, these maps are best suited for educational purposes, because a learner meeting a country for the first time needs the whole of it before the parts.
Classification By Purpose And Content
Maps can also be classified on the basis of their purpose and content, that is, by what the mapmaker set out to show rather than by how much the ground was reduced.
Three types are recognised on this basis. (a) Physical maps provide details about the natural features of an area or a country, such as its relief and its drainage. (b) Political maps portray different countries of the world along with their states, national and international boundaries, political units and administrative divisions. (c) Thematic maps show a particular feature or theme of the area, such as vegetation, climate or population density. All types of cultural maps, most of the atlas maps, and industrial, agricultural, military and linguistic maps fall in this category.
Fig. 1.1, Fig. 1.2 and Fig. 1.3 show one map of each of these three types, all of the same country.
Map
Fig. 1.1 Caption: A physical map, which shows the natural features of the area it covers. Brief: Physical map of India showing the full extent of India as officially defined; relief shown by colour tints with a height key in metres; major ranges, plateaus, plains and seas labelled; no state boundaries.
Map
Fig. 1.2 Caption: A political map, which shows boundaries and administrative divisions rather than relief. Brief: Political map of India showing the full extent of India as officially defined; state and union territory boundaries and names, national boundary distinguished from internal boundaries; no relief shading.
Map
Fig. 1.3 Caption: A thematic map, which maps a single theme — here the distribution of population. Brief: Thematic map of India showing the full extent of India as officially defined; states shaded in bands by total population in millions with the year of the data stated in the key exactly as printed; state figures labelled as in the original.
Fig. 1.4 pulls both schemes of classification into one tree, so that the whole of this section can be seen at once.
Flowchart
Fig. 1.4 Caption: Types of maps, classified in two ways — by content and purpose, and by scale. Nodes: Types of Maps → branch 1: Content and Purpose → physical maps; political maps; thematic maps. Types of Maps → branch 2: Scale → large scale → cadastral maps; topographical maps. Scale → small scale → atlas maps; wall maps.
1.4 Topographic Or Ordnance Survey Maps
The term ‘topography’ has been derived from two Greek words — ‘topos’, meaning ‘a place’, and ‘grapho’, meaning ‘to draw or depict’. The word therefore means the drawing of a place, and that is exactly what a topographical map does: it shows the surface of the earth in detail.
A topographical map is also known as a ‘Topographical Survey Sheet’, or simply a ‘topo-sheet’. The second name matters, because a topo-sheet is the record of a survey. Nothing on it is impression or estimate.
Why It Comes In Sheets
A single map of a whole country at this level of detail would be unusable, because the paper would have to be enormous. Topographical maps are therefore drawn on a number of sheets, where each sheet depicts the details of only one particular part of the whole area. These sheets are joined to give a complete picture of the entire area, in the way tiles make a floor.
Topographical maps are also known as Ordnance Survey maps, as these maps were originally drawn in Britain for the army under the direction of the Surveyor-General. These maps are now prepared in every country. In India, Ordnance maps are published by the Survey of India, Dehradun, in the Himalayan foothills of Uttarakhand.
How It Differs From A Physical Map
A topographic map is similar to a physical map in one respect, because it too shows different physical landscape features. The difference lies in how relief is shown. A physical map colours the land by height, while a topographical map uses contour lines to show changes in the landscape, and so it can show the shape of a slope rather than only its height band.
All topographical maps show two types of features, and both are on the same sheet.
The first are physical features, which include valleys, hills, plateaus, peaks, passes and waterfalls. These are depicted by contours, that is, the lines that join places having the same height above mean sea level. Mean sea level is the average level of the sea, and it is the zero from which every height on the sheet is measured.
By noticing the pattern and the density of the contour lines, we can determine the shape, the height and the gradient of a particular area, along with its specific features. Gradient here means the steepness of the slope, so contours crowded close together and contours spread far apart are telling you two different things about the same hillside.
The second are cultural or man-made features, which include roads, railways, bridges, buildings and canals. These are represented by symbols called conventional signs, and it is the key at the bottom of the sheet that tells you what each of them means.
Fig. 1.A4 sets the two out as a single classification, so that you can see that every mark on a topo-sheet belongs to one branch or the other.
Flowchart
Fig. 1.A4 Caption: Everything drawn on a topographical sheet is either a physical feature or a man-made one. Nodes: Topographical sheet → physical features → shown by contours → valleys, hills, plateaus, peaks, passes, waterfalls. Topographical sheet → cultural or man-made features → shown by conventional signs → roads, railways, bridges, buildings, canals.
We shall study contours and conventional symbols in detail in the next chapter. For the rest of this chapter, the question is a different one: once a feature has been found on the sheet, how is its position stated exactly?
1.5 Grid Reference
A grid is a set of lines used to find the exact location of places on a map. On an ordinary map, or on a globe prepared on a small scale, one can easily find out the position of a town with the help of the grid formed by latitude and longitude lines.
That method breaks down on a topo-sheet. Topographical maps are large scale maps, so exact locations cannot be expressed accurately by the grid of latitudes and longitudes. A single degree of latitude covers a great stretch of ground, and on a sheet that shows individual buildings, such a grid is far too coarse to point at anything.
To overcome this difficulty, a grid reference system is used. It comprises a square grid, with grid lines intersecting each other at right angles and numbered sequentially from the origin at the bottom left of the map. It indicates the location of a place in terms of a series of vertical and horizontal lines identified by numbers or letters.
Eastings And Northings
The points at which the vertical and horizontal lines of the grid cross are called coordinates. All these lines are numbered, and the numbering runs in a fixed direction, which is what makes the system work.
The vertical lines that increase in value eastwards are known as Eastings, and the horizontal lines that increase in value northward are called Northings. Fig. 1.5 (a) shows a set of eastings and Fig. 1.5 (b) a set of northings, drawn on their own so that the two sets can be told apart before they are put together.
Diagram
Fig. 1.5 (a) Caption: Eastings are the vertical lines, and their values increase towards the east. Brief: A plain rectangle crossed by four vertical lines numbered 31, 32, 33, 34 from left to right, with the numbers repeated at the top and bottom edges as on a survey sheet.
Diagram
Fig. 1.5 (b) Caption: Northings are the horizontal lines, and their values increase towards the north. Brief: A plain rectangle crossed by three horizontal lines numbered 8, 9, 10 from bottom to top, with the numbers repeated at the left and right edges as on a survey sheet.
These eastings and northings cut across each other to form squares, or grids. The origin of the grid system is in the South-West corner of the map, that is, the bottom left, so both sets of numbers grow as you move away from that corner. These lines are the basis for reference to landmarks and places shown on the map.
One rule governs every reference you will ever write. Whenever grid references are given, the eastings are given first and then the northings. Table 1.1 sets the two sets of lines side by side.
There are two types of grid reference, the four-figure grid reference and the six-figure grid reference, and the difference between them is one of precision.
Four-Figure Grid Reference
The four-figure grid reference is used to find out the location that lies within a particular square. In this type of reference, the first two figures give the eastings, whereas the last two give the northings.
It suits features that are not points at all. Large lakes, meanders, streams, settlements, embankments and physical features occupy some space on the map, and naming the square they lie in is the honest way to locate them. Fig. 1.6 (a) shows such an extract.
Map
Fig. 1.6 (a) Caption: A four-figure reference names the square a feature lies in, not a point inside it. Brief: Topographical sheet extract, scale and contour interval as printed on the original; eastings 43 to 45 and northings 85 to 87 numbered on all four edges; the square with easting 43 and northing 85 outlined; the settlement of Hebatpur and the other settlements, road, tank and bench mark symbols of the original all legible.
Four digits have replaced a description. Anyone holding this sheet can now find Hebatpur without being told that it lies near a road or beside a tank. What those four digits cannot do is take you to a doorstep, because the square they name is a kilometre wide, and a settlement is only one of the things inside it.
Six-Figure Grid Reference
To get the six-figure grid reference, divide the square into ten equal parts vertically and then horizontally. You will now get the third figure in the eastings and the sixth figure in the northings. The first three figures are the eastings and the last three are the northings.
The gain in precision follows from the arithmetic of that division. Each square on the ground is 1 km across, and
\[\text{Side of one tenth} = \frac{1000\ \text{m}}{10} = 100\ \text{m}\]
where 1000 m is the side of one grid square in metres and 10 is the number of equal parts it has been divided into. The six-figure reference thus obtained gives the location of a place to the nearest 100 metres.
Study Fig. 1.6 (b), in which one square has been subdivided in this way.
Map
Fig. 1.6 (b) Caption: The square is divided into ten parts each way, and the third and sixth digits say which part the feature falls in. Brief: Topographical sheet extract, scale and contour interval as printed on the original; eastings 25 to 27 and northings 89 to 91 numbered on all four edges; one square outlined and subdivided into ten parts vertically and horizontally with the tenths numbered 1 to 10 as in the original; the settlement of Kheda, the temple north-east of it, and the tank, road and spot height symbols of the original all legible.
The extra two digits change what the reference can be used for. A four-figure reference would have put the temple somewhere in a square a kilometre wide; 265902 puts it within about 100 metres, which is close enough to walk to. That is why spot heights, bench marks, causeways, temples, post offices, police stations, wells and bridges are located with the help of the six-figure grid reference — each of them is a point on the ground, and a point deserves a point reference.
1.5.1 Importance Of Six-Figure Reference
The six-figure reference matters for two connected reasons. It helps in pin-pointing a place or an object on the map nearest to 100 metres, while it also adds greater accuracy to the map itself, because every small feature on the sheet can now be given a position that is exact rather than approximate.
Accuracy of this kind is not a refinement. A repair party, a survey team or a relief van needs to arrive at a place, not near it, and a reference that is right to within 100 metres is what makes the difference between the two.
1.6 National Grid Reference
A grid reference fixes a place inside a sheet. A different question comes first: out of the hundreds of sheets that cover a country, which sheet is the one you need? That is what the national numbering system answers.
The Survey of India (SOI) was set up about a hundred years ago by British Surveyors. ‘Open Series Map’ have been introduced as per the National Map Policy of 2005 by Survey of India, and along with them a new map numbering system based on the International Map of the World (IMW) has been adopted.
How A Sheet Number Is Built
The system works by cutting the earth’s surface into larger blocks and then cutting each block again, so that every extra character in the number narrows the ground it refers to.
The rules of the numbering system are as follows. (a) The IMW numbering system, with minor modification, is used up to the 1°×1° or 1:250,000 scale, so the system covers everything from a very large block of the earth down to a sheet of that size. (b) Since the IMW map number for India will always start with ‘N’, India being in the northern hemisphere, the first letter is omitted. A letter that never changes carries no information, so it is dropped. (c) The next alphabet and number of the IMW map number denotes the 6°×4° region of the IMW series. The letters run northward from the equator, and ‘A’ begins from the equator to 4°N latitude. (d) Each 6°×4° rectangle is further subdivided into 24 squares of 1°×1°, since a block 6° wide and 4° tall holds six columns and four rows of such squares. Each square is indicated serially by an alphabet increasing first towards east and then towards south, starting with ‘A’. (e) Each 1°×1° square is further divided into 16 squares of 15’×15’, that is, 15 minutes by 15 minutes. A minute is one-sixtieth of a degree, so 15 minutes is a quarter of a degree, and four rows of four such quarters fill the square. Each square is indicated serially by a number increasing first towards south and then towards east, starting with ‘1’, which is similar to the system adopted in India and Adjacent Countries.
Fig. 1.A5 shows the three cuts as one chain, from the largest block down to the sheet in your hand.
Flowchart
Fig. 1.A5 Caption: Each step in the number cuts the ground smaller, and the sheet number records every cut. Nodes: IMW number for India starts with ‘N’ → first letter omitted → 6°×4° region, given by a letter and a number → subdivided into 24 squares of 1°×1°, lettered from ‘A’ eastwards then southwards → each divided into 16 squares of 15’×15’, numbered from ‘1’ southwards then eastwards → the map sheet number
Fig. 1.7 shows the whole scheme laid over the country, with the successive subdivisions drawn as insets.
Map
Fig. 1.7 Caption: The national grid reference scheme of the Survey of India, with each block subdivided into smaller sheets. Brief: Map of India showing the full extent of India as officially defined, on the projection, datum and scale printed on the original; the 6°×4° blocks lettered and numbered across the country as in the original; insets showing one block subdivided into 1°×1° squares and one of those subdivided into 16 numbered squares, with the same square picked out in both insets as printed.
Tracing One Sheet Number
Read backwards, the number is an address. ‘G-43’ names a block of the earth’s surface, the ‘S’ names one square degree inside it, and the ‘10’ names a quarter-degree square inside that. Anyone who knows the rules can go from a latitude and longitude to a single sheet without a catalogue, and from a sheet number back to the patch of ground it covers.
1.7 Summary
- The earth is too large and too spherical to be seen whole or to be shown as it is on a flat surface, so we work with models of it — the globe and the map.
- A globe is a three-dimensional representation of the earth and the only true one, indicating shape, direction, area and other features correctly, but it has limits.
- Its surface is small, so it cannot show physical features and other characteristics in detail.
- Topographic details cannot be shown on it at all.
- Cartography is the art and science of mapping, by which three-dimensional features such as mountains, valleys and rivers are drawn on a uniform basis on a flat sheet.
- A map is a representation of the earth’s surface, or a part of it, showing natural or man-made features, drawn to scale on a flat surface, and it lets us study phenomena such as soil, climate, vegetation, rivers, mountains, volcanic eruptions and earthquakes together with their inter-relationships.
- Every map is built from six elements, and a reader looks for all six.
- The title says what has been mapped.
- The scale gives the relationship between map distances and ground distances.
- Direction refers to the cardinal directions, with north conventionally at the top.
- The grid system is the network of lines that pinpoints a location.
- Conventional signs are the graphic language in which features are drawn.
- The key, or legend, explains what those signs mean.
- Maps are classified on the basis of their size into large scale and small scale maps.
- Large scale maps include topographical maps, prepared by the Survey of India on scales of 1:50,000 and 1:25,000, and cadastral maps, which record property and field boundaries for public record.
- Small scale maps include wall maps, meant to be viewed at a glance, and atlas maps, which give a condensed and generalised picture and are best suited for educational purposes.
- Maps are also classified on the basis of their purpose and content into physical maps, political maps and thematic maps.
- A topographical map, or topo-sheet, shows the surface of the earth in detail; it is drawn on many sheets that join to cover an entire area, and in India these Ordnance maps are published by the Survey of India, Dehradun.
- Every topographical map carries two kinds of feature.
- Physical features, shown by contours, which are lines joining places of the same height above mean sea level, and whose pattern and density reveal shape, height and gradient.
- Cultural or man-made features, shown by symbols called conventional signs.
- Because latitude and longitude are too coarse for a large scale map, a square grid is used, numbered from the origin at the south-west corner; the vertical lines increasing eastwards are eastings and the horizontal lines increasing northwards are northings, and eastings are always read first.
- A four-figure grid reference names the 1 km square a feature lies in, which suits features that occupy space, such as settlements, lakes, meanders and embankments.
- A six-figure grid reference divides that square into ten parts each way, fixing a place to the nearest 100 metres, and is used for point features such as spot heights, bench marks, temples, post offices, police stations, wells and bridges.
- Under the National Map Policy of 2005, Survey of India sheets are numbered on the International Map of the World system, each step of the number cutting the ground finer — a 6°×4° region, then a 1°×1° square, then a 15’×15’ square.
Flowchart
Fig. 1.A6 Caption: The whole chapter as one chain — from the earth itself to a number that names a hundred-metre patch of it. Nodes: The earth, too large to see whole → globe: true shape, no detail → map: a part of the surface, drawn to scale, detail visible → classified by purpose and content → physical / political / thematic. Map → classified by scale → large scale → cadastral / topographical → topographical sheet → physical features shown by contours; cultural features shown by conventional signs → which sheet? → national grid reference: 6°×4° region → 1°×1° square → 15’×15’ square → where on the sheet? → square grid of eastings and northings → four-figure reference: the 1 km square → six-figure reference: to the nearest 100 metres
What This Chapter Cannot Tell You
A grid reference is only as good as the sheet it is read from. It gives a position, but it says nothing about what is at that position now, because a topo-sheet records the ground as it was on the day of the survey, and roads, buildings and canals change after that.
The scale sets a floor under the precision as well. Six figures reach 100 metres and no further, so a sheet at 1:50,000 can point you to a field but not to a corner of it, and anything smaller than the symbol drawn for it has been generalised away.
This chapter also shows only how position is stated. What the shape and spacing of the contours actually mean on the ground, and how each conventional sign is to be read, are matters for the next chapter. ## 1.8 Check Your Concepts
- Study the classification in Fig. 1.4 and answer both parts.
- Name the category to which cadastral maps belong and the category to which atlas maps belong.
- Explain why a cadastral map has to be drawn on a large scale, while an atlas map does its work on a small one.
- A grid square on a topographical sheet is 1 km across. Show, step by step, how dividing that square into ten equal parts vertically and then horizontally gives a location accurate to the nearest 100 metres.
- Table 1.1 states that the easting to the left of an object is read and the northing below it is referred, and that eastings are always given first. Explain what would go wrong if one reader gave the northings first while another followed the rule.
- Fig. 1.3 maps population by state. State one thing the map shows clearly and one thing it cannot show, and explain how the scale at which it is drawn accounts for both.
- What is the National Grid Reference (NGR)?
1.9 Case-Based Questions
- Questions (a) and (b) are to be answered from the map extract in Map 1.1.
Map
Map 1.1 Caption: The map extract to be used for the grid reference questions in this exercise. Brief: Topographical sheet extract, scale and contour interval as printed on the original; eastings 58 to 63 and northings 29 to 34 numbered on all four edges; the settlements, the main river and Dior Nadi, the causeways, the siphon, the aqueduct, the area of brackish water, the annual fair grounds, the rocky knob, and the post office, dispensary, police station, hospital and surveyed tree symbols of the original all legible, with the key needed to read them.
- Give the four-figure grid reference of the following from the given map extract:
- Two settlements having a post office.
- Two settlements having a dispensary.
- The siphon.
- The confluence of the main river and Dior Nadi.
- The area of brackish water.
- The annual fair grounds west of Malgaon.
- Give the six-figure grid reference of the following from the given map extract:
- The police station.
- 4r near the rocky knob.
- The post office at Malgaon.
- The surveyed tree at Posintra.
- The dispensary north of Posintra.
- The hospital near Pamera.