Interpretation of Topographical Maps

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topographical survey sheets 14 Legend 15 Glossary of conventional signs and symbols used in survey maps INFORMATION IN THE MARGINS i The number of the topo sheets Topo sheets numbers can give an idea as to which part of India is shown on the map For example topo sheet numbers 45D 7 45D 10 and 45 F 3 show parts of Gujarat

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Contours are shown at regular vertical,intervals , On a 1 50 000 map the interval is 10 m . INTERPRETATION OF CONTOURS, The shape of the contours indicates the. shape of the ground ,When contours are further apart the slope. is gentle and when contours are close,together the greater the drop . When contours are equal distance apart the,slope is uniform .
a Contours are continuous No matter how,far they travel they always return to where. they started Except for a cliff ,b When spacing of contours down a slope. gets close together at the bottom the slope,is convex . c When spacing is further apart the slope,is concave . STAGE 3 PLOTTING GRID, REFERENCES, A grid is a rectangular square system of.
lines superimposed on a map within which, any point can be located . Maps are normally printed so that north is, North South lines are called Eastings. because the numbers increase as they go, East West lines are called Northings. because the numbers increase as they go,What are the 3 points in determining. 1 bench marks ,2 trig points and,3 spot height , What are Eastings and Northings .
1 Eastings run move left to right and, 2 Northings run bottom to top . What are the two most important things to,remember when giving a grid . 1 Easting value first and,2 never round up ,What is the purpose of a contour line . Joins points of equal heights , A topographic map is a type. of map characterized by large scale detail,and quantitative representation of relief .
usually using contour lines in modern,mapping but historically using a variety of. methods Traditional definitions require a,topographic map to show both natural and. man made features , The Centre for Topographic Information. provides this definition of a topographic,map A topographic map is a detailed and. accurate graphic representation of cultural,and natural features on the ground .
According to Cartographer s Kraak and,Ormeling Traditionally the main division. of maps is into topographic and thematic,maps Topographic maps supply a general. image of the earth s surface roads rivers ,buildings often the nature of the. vegetation the relief and the names of the,various mapped objects . The study or discipline of topography ,while interested in relief is actually a.
much broader field of study which takes,into account all natural and man made. features of terrain , Topographic maps have multiple uses in. the present day any type of,geographic planning or large . scale architecture earth sciences and many,other geographic disciplines mining and. other earth based endeavours and,recreational uses such as hiking or in.
particular orienteering which uses highly,detailed maps in its standard requirements . Map conventions, The various features shown on the map. are represented by conventional signs or,symbols For example colors can be used. to indicate a classification of roads These,signs are usually explained in the margin. of the map or on a separately published,characteristic sheet .
Topographic maps are also commonly,called contour maps or topo maps In the. United States where the primary national,series is organized by a strict 7 5 minute. grid they are often called topo quads or,quadrangles . Topographic maps conventionally,show topography or land contours by. means of contour lines Contour lines,are curves that connect contiguous points.
of the same altitude isohypse In other, words every point on the marked line of. 100 m elevation is 100 m above mean sea,There are several rules to note when. viewing topographic maps , The rule of V s sharp pointed vees. usually are in stream valleys with the,drainage channel passing through the point. of the vee with the vee pointing upstream ,This is a consequence of erosion .
The rule of O s closed loops are normally,uphill on the inside and downhill on the. outside and the innermost loop is the,highest area If a loop instead represents a. depression some maps note this by short,lines radiating from the inside of the loop . called hachures , Spacing of contours close contours. indicate a steep slope distant contours a,shallow slope Two or more contour lines.
merging indicates a cliff , Of course to determine differences in. elevation between two points the contour,interval or distance in altitude between. two adjacent contour lines must be,known and this is given at the bottom of. These maps usually show not only the,contours but also any. significantstreams or other bodies,of water forest cover built up areas or.
individual buildings depending on scale ,and other features and points of interest . Today topographic maps are prepared,using photogrammetricinterpretation. of aerial photography Older topographic,maps were prepared using. traditional surveying instruments , In most cases contour intervals are. consistent throughout a map Sometimes,dashed contour lines are present these.
represent half the noted contour interval , Understanding Topographical Maps. Understanding of surface depends on the,ability to interpret topo maps They . Are based on accurate surveys , Show a variety of landforms with. carefully chosen symbols signs , Shows natural features like hills valleys . waterfalls , Also show man made features like roads .
railways buildings bridges and canals ,TOPOSHEETS ARE . Are prepared on a number of sheets since,they are large scale maps . Each sheet gives the details of a part of,the whole area . When these joined together they form a,map of the whole area . INTERPRETATION OF TOPO MAPS, AND SURVEY MAPS,IT involves ability to follow the symbols.
portrayed in the map , Understand the information given in. pictorial and written form, Visualize the topography of the original. area by interpreting the contour, Spot heights skillfully. Map reading is a practical skill , Can be developed only by reading topo. map very minutely and mentally analyzing,the details with the help of conventional.
signs symbols given in their,conventional colours . As the conventional symbols cannot cover,all the graphical details each. topographical map sheet provides the,necessary information in the margin for the. 1 Identification of topographical maps,2 Reading the Grid reference. 3 Scale R F ,4 Representation of Relief by contours.
5 Directions,6 Measuring distances and calculating. 7 Drainage, 8 Man made and natural features,9 Means of transport in relation to relief. 10 Land use and irrigation,11 Settlements,12 Inferring occupations. 13 Importance of colours and tints in,topographical survey sheets. 14 Legend,15 Glossary of conventional signs and,symbols used in survey maps.
INFORMATION IN THE MARGINS,i The number of the topo sheets Topo. sheets numbers can give an idea as to,which part of India is shown on the map . For example topo sheet numbers 45D 7 ,45D 10 and 45 F 3 show parts of Gujarat. and Rajashthan , Knowing the number of toposheet can. give us a clue about the general physical,relief of the region and its climate which.
can be confirmed by other information,given in the map . Eg since all toposheets are from India it,may be inferred that all the reigons. represented by those topo sheets would,have a tropical monsoon climate with. seasonal rainfall , Western Rajasthan u may expect scanty. rainfall a fact which could be verified by,the presence of dry river beds and.
disappearing streams , 45D 7 shows a region of northern Guj . closer to the border of Rajasthan, 45D 10 lies in the southern part of. Rajasthan close to the border of Gujarat, 45F 3 lies in the western Rajasthan near. 53B 7 shows a region in Punjab close to,the border of Haryana . 56D 11 shows a region in north east,Karnataka , 64P 13 shows a region in north east.
ii Latitudinal and Longitudinal extent ,These indicate in whichpart of the Earth. the area is located , On a 4 degree topographical map at least. 4 lines of latitude and longitude can be, seen But as the scale of the topo map. increases the number of latitudes seen on,the map decreases . GRID REFERENCE, A Grid is a set of lines used to find the.
exact location of places on a map , The National Grid Reference is a system. of rectangular co ordinate , The origin of the grid reference lies at a. point in the south west corner of the map , Thus any place on the map can be located. by starting its distance east or north of the,origin of the grid reference . Topo maps bear the national grid of,squares drawn to the scale of 2 cm 1km.
with each square having a side measuring, These are sheets most commonly used for. various purposes and are of vital practical,importance .

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