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Map Scale

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Map Scale

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    1. Map Scale

    2. Scale Ratio between distances on a map or globe, and their actual ground distances.

    3. Expressions of scale Graphic scale (scale bar) visual expression line marked off in units Good for making rough estimates of distance

    4. Estimating Distance using Graphic Scale Mark off map distance using piece of paper Estimate distance using the scale bar.

    5. Expressions of scale, cont. 2) Statement of scale Verbal expression Ex. One inch represents ten miles Easy to understand

    6. Expressions of scale, cont. 3) representative fraction (RF) mathematical expression written as a ratio (sometimes as a fraction) ex. 1: 24,000 (same as 1/24,000) map distance unit : ground distance unit 1 : (some value) independent of units Good for more precise calculations of distance But you usually have to convert your answers for them to be meaningful Ex. How far is 24,000 inches?

    7. English System Conversions Inches to miles divide by 63,360 Feet to miles: divide by 5,280 Inches to feet: divide by 12 Miles to inches: multiply by 63,360 Miles to feet: multiply by 5,280 Feet to inches: multiply by 12

    8. Distance Calculations using Scale 1) Set up ratio md md ---- = ----- gd gd md is map distance; gd is ground distance one represents scale and the other is the distance between two places.

    9. Solving scale problems, cont. Rules a) three values are known, insert these values and their units of measure (if given) b) units for numerators must be the same c) units for denominators must be the same 2) Solve for the unknown value not necessarily the final answer Convert into appropriate unit of measure, if required

    10. Example Scale Problems 1) The map distance between two towns is 10 inches on a map whose scale is 1:24,000. How far apart are the towns? md/gd = md/gd 1/24000 = 10”/x 1”/24000”=10”/x” 1*x = 24,000*10, or x = 240,000” 240,000”/63,360”per mi = 3.78 mi

    11. 2) Two towns are 15 miles apart and shown four inches apart on a map. a) what is the statement of scale? 4”/15mi = 1/x 4”/15mi = 1”/x mi 4x=15, so x = 3.75 mi one inch represents 3 3/4 miles b) what is the RF? 1”/3.75mi = 1/x 3.75 mi * 63,360 in/mi = 237,000 in RF is 1:237,000

    12. Relative Scale The larger the scale, the closer the map comes to reality. Scale Mapped Area RF denom large little, yet detailed small small great, yet general large

    14. Homework

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