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Chapter 1 Map Reading. Chapter 1: Map Reading. What is a topographic map ? Large-scale map representing selected aspects of the earth’s surface Shows both physical and human features Components of a topographic map Title Grid lines Names of places Scale Direction Contours - PowerPoint PPT Presentation

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• Chapter 1

• What is a topographic map ?Large-scale map representing selected aspects of the earths surfaceShows both physical and human features

Components of a topographic mapTitleGrid linesNames of placesScaleDirectionContoursLegend and symbolsChapter 1: Map Reading

• Chapter 1: Map ReadingSome basic components of a topographic mapTitlePlace nameGrid linesScaleContourSymbols

• Grid linesEastings vertical lines that run from west to eastNorthings horizontal lines that run from south to northGrid lines are numbered to provide the coordinates of specific features on a map

Grid referenceSet of digits formed using the grid values of eastings and northingsDefines a location on a mapThe more digits in a grid reference, the more precise the location, e.g. a six-figure grid reference gives a more accurate location than a four-figure grid referenceChapter 1: Map Reading

• Four-figure grid referenceIdentifies a specific grid squareFirst two digits = Value of the easting on the left of the squareSecond two digits = Value of the northing at the bottom of the squareExample:The four-figure grid reference for Point X is 6530.Chapter 1: Map Reading

• Six-figure grid referenceIdentifies a specific point in a grid squareHow:Determine the four-figure grid referenceDivide the space between the two eastings of the grid square into ten equal intervalsCount how many tenths the point is from the left to right add this number after the first two digits of the four-figure grid referenceRepeat Step 2 for the northings of the grid squareCount how many tenths the point is from the bottom up add this number to the end of the grid referenceExample:The six-figure grid reference for Point X is 655305Chapter 1: Map Reading

• ScaleShows what a certain distance on the map represents on the land in the real worldThree ways to indicate scale on a map:Line scale E.g.

Word statement E.g. 1cm on the map equals 30km on the ground

Representative fraction E.g. 1:50,000 means that one unit on the map represents 50,000 units on the ground in the real worldChapter 1: Map Reading

• Place a strip of paper on the line between the two pointsMark the two points on the edge of the paper strip3.Place the marked edge of the paper strip on the line scale4. Read the distance between the two pointsReading the straight-line distance between two pointsChapter 1: Map Reading

• Place one end of a string at one end of the path to be measured (point C)Using the string, trace the curved pathMark the end of the path on the string (point D)Place the string on the line scaleRead the distance off the scaleReading the length of a curved pathChapter 1: Map Reading

• DirectionTwo ways to describe the direction of a placeUsing compass points Cardinal points of the compass: north, south, east, west Intercardinal points: northeast, southeast, southwest, northwest

Using bearings Direction of a place is expressed as an angle (in degrees) clockwise from the base direction (0) Base direction could be grid north, magnetic north or true north

• Grid northDirection of the vertical grid lines (called eastings) on a mapMagnetic northDirection of the magnetic north pole

True northDirection of the geographic north poleChapter 1: Map Reading

• Land elevationContours Lines on the map joining places with the same height The number on a contour line indicates the height that the line represents

Spot heights Points on the map showing the heights of hillsChapter 1: Map Reading

• Benchmarks Marked points of known elevation which serve as reference points from which the height of other places may be established

Trigonometrical stations Points marked by metal discs mounted on stable foundations such as concrete pillars Usually located on top of mountains or hills May be used as benchmarks for measuring elevationChapter 1: Map Reading

• Recognising relief featuresThe shape of contour lines and the spacing between them show us the shape, height and slope of relief featuresChapter 1: Map ReadingA plateauA mountainUndulating relief

• Chapter 1: Map ReadingA gentle slopeA stepped slopeA steep slope

• River featuresTopographic maps can give us some information on the river features of an areaRiver source Point where a river originatesRiver mouth Point where a river endsRiver course Path followed by a river Perennial course flows throughout the year Indefinite or seasonal course flows only during certain seasonsWatershed Boundary between two drainage basinsChapter 1: Map Reading

• Drainage pattern Pattern formed by the rivers in a particular drainage basinChapter 1: Map ReadingTrellis patternDendritic patternCentripetal patternRadial pattern

• Cross-sectionsDrawing cross-sections will help you identify relief featuresHow:Draw a line (XY) across the map where the cross-section is to be drawn.Chapter 1: Map Reading

• Place a strip of paper on the line XY. Moving from left to right, mark each point on the edge of the paper where XY meets a contour.

Chapter 1: Map ReadingOn another piece of paper, draw the horizontal and vertical axes for the cross-section. The horizontal axis should be the length of XY. Choose a suitable scale for the vertical axis.

• Place the marked edge of the paper strip (from Step 2) along the horizontal axis of the cross-section graph. For each mark on the paper strip, draw a vertical line up to the equivalent height and mark off with a dot.

Chapter 1: Map ReadingJoin all the dots with a smooth curve to complete the cross-section of XY.

• GradientTells us how steep a slope isTo calculate gradient:Vertical distanceGradient = Horizontal distance A gradient of 1:25 means that for every horizontal distance of 25 units covered, you would ascend one unitChapter 1: Map Reading

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