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Geography 12: Maps and MappingLecture 10:

Cartometry: Lines and Areas

Line and Area features on topo maps

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Land surveys and roads

A “length” datum

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Railroads

Lines and areas

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More water

Ice and snow

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Watery symbols

Surface features

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Contours: Whole separate lecture

Distance measurement: from the ground

• Pacing• Survey

– Chain/Pole– Wheel– Stadia– EDM– GPS

• Tape• Triangulation• Ships log

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Distance on the ground

• Odometer• GPS point trace• Dead reckoning• Record coordinates and compute

Pacing

• Measure a base line using a superior method

• Devise method for pace counting• Repeat measurement several times• Average result and divide for length of

pace• Note how pace varies with terrain

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Measuring on the map

Length from coordinates

(x1, y1) (xnpts, ynpts)

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Area measurement: From the mapPolar planimeter

James Clerk Maxwell (1855)

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Four methods for area

For example, Lake Los Carneros

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Area from coordinates

Equivalence