Lecture+ 5 map interpretation _measurements_

8/17/2019 Lecture+ 5 map interpretation _measurements_

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Lecture 2By g.a.b. yiran


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Measurement on maps contd


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Determination of Location orPosition

• We can determine the position of a town accuby approximation.

• Accurate location is done by mathematical calto determine exactly where the point is. E.g. Uof hana is located on Lat. !" #$%&' long. $" ($

• )he approximate location is done using relativvalues that indicate approximately where a pofound

• *f for instance' you are driving around town anwant where a +lling station is or you are a touwant the nearest tourist centre to your hotel' not need the exact location of these facilities.case' you can say the +lling station is about ,$of -edi house' &rumah mausoleum is in Accracould also re+ne the location using a referenc


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• 0elative Location of a city or destination on the planerelationship to nearby landmars. )hat is' you de+ne

in relation to another element or system' which couldlandmar' direction' or time. As an example' 1umasi inorth of Accra. 3ere we have used both time and dire

• Absolute Location is the de+nitive location of a place recogni4ed coordinate system in terms of latitude and

or grid reference. 5or example' Legon is located !"(67$"287 West.

• rid reference system refers to a system of vertical ahori4ontal lines that are drawn across the face of the divide the map into s9uares for easy reference. )hesenumbered or lettered from a chosen origin and the nu

written against the lines at the edges of the map.


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• 5our +gure reference

• )his is a 9uic and easy way of identifying thewithin which a place can be found.

• 5or example' if the four +gure grid for -ity ca#82#' then the #8 is the easting of the s9uare-ity campus and 2# is the northing as shown

•

3ere unless the point is located at the interseboth the eastings and northings' the exact pooften not de+ned but rather it de+nes a framewithin which the point could be located and tdoes not give precise position.


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5our +gure• &ote that the +rsthe bottom left cogrid lines #: and last s9uare at the

corner is 2$ and 2+gures de+ne thecorner of the s9u

• *f you have so main a s9uare' all thfeatures will be g

same value. 5or e-ity campus and

• in the 5ig. will ha#82# as their posis di>cult to di?ethem. )he 6 +gursolve this problem

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41

42

43

44

37 38 39 40 41

-ity campus

Accra Poly


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=ix +gure reference

• 5or example' if you are to locate -ity-ampus in 5ig. above with gridreference of #862#2 you +rst identifythe s9uare in which -ity -ampus islocated. *n this case' it is within the

s9uare #82#.• /ou then divide this s9uare intotenths both vertical and hori4ontal toform smaller s9uares as in 5ig. below

• Locate the s9uare that contains thepoint and use the sub@grid closer tothe point.

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41

42

4344

37 3839

-ity -aAccra Po

• Let us tae the s9uare in which -ity -ampus is

divide it into tenths. &ote it is the same box bbeen ex anded to let ou see the divisions &ot


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Bathematical location

•

)his is the determination of the position of a point on a ma coordinate system.

• We have two types of coordinate system the geographicsystem and the rectangular coordinate system. )hese wiin detail later but we use them at this stage to locate our

• )o determine the mathematical position or the exact or aposition of a place' use the steps that follow to measure

coordinates• )o measure or determine the coordinates' +rst determinewhich you will use to represent the feature. *f it is a pointhen you have no problem' but if it is an areal feature' yodetermine an appropriate point. )his could be the town c

Cunction' chief%s palace' etc.

• &ext' you locate the grids line within which the feature fa

• Draw lines connecting these grids if they are not on the mbe careful with drawing these lines and clean them after


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• Draw a vertical and hori4ontal lines through the centre of tcut the grid lines that you Cust drew.

• Beasure the distance between the latitude and the longituthe map with a rule.

• Beasure the distance from the smaller grid value to the poline through the town cuts the gridlines. =o you measure frpoints to the hori4ontal and vertical lines through the town&ote that the lines passing through the point are the latitulongitude of the point.

•

5ind the di?erence between the latitude grids and the long• Use proportions to calculate the latitude di?erence and thedi?erence.

• Use the formula Latitude or longitude di?erence

• ;Distance measured from lower grid to hori4ontal line


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• Example determinethe location of DormaaAhenro on the map

• Distance betweenlatitudes 2.2cm

• Distance betweenlongitudes !.Fcm

• Di?erence betweengrid latitudes :"#$%@:",$% $"(!%

• Di?erence betweengrid longitudes#"$$%@ $"2$% $",$%


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• Distance between the lower latitude and latitude pathrough the point $.2cm

• Distance between the lower longitude and longitudethrough the point #.6cm

• Di?erence between lower latitude and latitude passpoint $.22.2x$"(!% $.$8$( x $.,! $" (!% $" ($"$(%,(G

• Latitude of Dorma Ahenro :"(!%$$G H $"$(%,(G

• Di?erence between lower long. and long. passing th #.6!.Fx$",$% $.6,$: x $" ,$% $"(,.2(2% $"(

• Longitude of Dorma Ahenro $"2$%$$G H $"(,%,!G$"!,%,!GW

• )he coordinates of Dorma Ahenro is latitude :"(6%,longitude $"!,%,!GW

Pl i P i h B


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Plotting a Point on the Bap• Plotting a point is the reverse operation of meascoordinates on a map

• 3owever some of the steps outlined above are re

while some remain the same. =o the steps that areversed are outlined below

• )he same formula as above is used

• We now the latitude and longitude of the pointshave to determine the distances between them a

so we can measure and plot.• 5irst the determine the grids within which the w

• Beasure the distance between the grids

• Determine the latitude di?erence from the latitupoint and the lower grid latitude

• Do same for the longitude di?erence


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Plotting a Point on the Bap

• )he intersection of the lines representing the lat. and long sholocation of the point

• Example locate a point with lat. :" ,,% ($G&' and long. ," #8% 2• )his point falls between latitudes :" #$% $G& and :" (!% $G& an," ,$% $GW and ," 2$% $GW.

• lat. di?erence of grids :" #$% $G @ :" (!% $G $" (!% $G $.,!

• long. di?erence of grids ," 2$% $G @ ," ,$% $G $" ,$% $G $.#

• lat. di?erence of lower grid and point :" ,,% ($G @ :" (!% $G

$.((82"• long. di?erence of grids ," #8% 2(G @ ," ,$% $G $" (8% 2(G

• Distance between lat. grids 2.2cm

• Distance between long. grids !.Fcm

• Distance between lower lat. and lat. of point ;$.((82.,!


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Plotting a Point on the Bap

5.7c

5.7

2.1cm

• Distance between lower

long. and long. of point ;$.#,F(.####


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Beasuring height

•

heights of the ground are represented on the mcontours or spot heights.

• )herefore' if a point falls exactly on the contouheight' the contour or spot height value is taeheight of the point.

•

*f on the other hand' it does not fall on the conwill have to measure the height by interpolatio

• =uppose we want to +nd the height of point ;dolabelled - in the diagram' +rst measure the shopossible distance between the contours within point falls.


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Beasuring height

•

=uppose we want to+nd the height of point;dot< labelled - in thediagram' +rst measurethe shortest possibledistance between the

contours within whichthe point falls.

•3ere it falls between,$$m and #$$mcontours.


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Beasuring height• )he distance from the ,$$m contour to the po$.2Fcm

• Distance between contours (.,:cm

• )he di?erence between the ,$$ and #$$m ;i.einterval < #$$ I ,$$ ($$

• 3eight di?erence

x

• 3eight di?erence x ($$ #:.F

• 3eight of point lower contour H height di?e,$$ H #:.F ,#:.Fft

• &ote the hei hts in the + ure were iven in fe

Distance from lower contour to point

Distance between contours

-rin

l$.2F(.,:


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=ection or Pro+le Drawing

•=ection or pro+le drawing is usually

to show how the land surface will loif it is cut to the mean sea level or areference level

•Draw the line connecting the points

between which the section is to be say line AJ

•Place a thin piece of paper along thAJ

•Bar o? where the contours cross t


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=ection or Pro+le Drawing• 0emove the paper and place along the base of thpaper where the section is to be drawn

• )ransfer the mars onto the graph

• Draw vertical lines proCecting from the mars on

• -hoose an appropriate vertical scale using the rebetween the vertical scale and hori4ontal scale cavertical exaggeration ;i.e. vertical exaggeration

scalehori4ontal scale and this should be around • Use the vertical scale to plot the heights on the vlines you proCected from the mars

• Koin the points with a line drawn with freehand

• &ote where the line crosses a landmar' indicate


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=ection or Pro+le Drawing

A

J

=uppose it l

( $ $

, $ $

# $ $

2 $ $

! $ $

! $ $

A

di t =l


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radient or =lope• radient or slope of a line is de+ned as the ratio overtical interval to the hori4ontal e9uivalent.

• ertical interval is the di?erence in height betweepoints and the hori4ontal e9uivalent is the hori4ondistance between the same points.

• radient vertical intervalhori4ontal e9uivalent

• 5or example' calculate the slope of the land betweregistry with height (!8m and the gate with heigh

and the distance between them is (m.• =olution

• Di?erence in height ;vertical interval< (!8 @(!$

• Distance between registry and gate ;hori4ontal e9 (m ($$$m

• 8 ($$$ $.$$8 or $.8M

Uses of Beasurements


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Uses of Beasurements• Distance

(. )o calculate areas of regular features

,. )o tell how far one feature is from another

#. )o determine the cost of certain proCects. e.g. the road can be determined if the length of the road issimilarly the cost of laying a pipe from a water souconsumer can also be estimated' etc.

2. Nther applications exist in baning' telecom' elect

transport' etc. give scenarios under which these awill need to now distance

•.Jearings

(. Jearings are use to now the direction of travel. )particularly useful in air@Oight and sea navigation

pilots or captains use the bearing between the ori

U f B


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Uses of Beasurements• Area

(. Agriculture areas are measured to determine' for efarm si4es' irrigable area of an irrigation proCect' cr

9uantity of fertili4er' cost of tractor plough' etc.,. Urban studies )he area of a city can be measured o

period for the city authorities to study the rate of gthe city and therefore tae necessary steps to curtagrowth if it is out of hand

#. Population studies for population density calculatioPopulation density may be used to determine whethplace is overpopulated or not. *n case of over populresettlement plan can be made and the si4e ;i.e. areland re9uired for the resettlement can be measuredfrom the map.

2. 5orestry here' areas of forest reserves are calculat

U f B t


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Uses of Beasurements

• 3eight and section drawings

(. -onstruction *n road construction' these measure

used to +x the level of a road and therefore deteramount of cut or +ll where necessary.

,. )hey are also used to +x vertical curves of roads

#. )o determine the amount of excavation or embanneeded in the construction of a reservoir or a dam

respectively.2. Limit human activities farming and human settlem

allowed to tae place above a certain gradient aloand therefore above the stipulated slope allowanccountry' a forest reserve may be established to prhuman activities from going on there.

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Lecture+ 5 map interpretation _measurements_