1. The Earth is Not Flat! Latitude and Longitude give us locations on Earth (or other planets). How do we show the third dimension?

2. Elevation is referenced to…? The distance from the center of the Earth would be most accurate but is hard to measure and is distorted by the oblateness of the planet. The most frequent standard is Sea Level. By hopping measurements from the coast we can get this. GPS can actually measure just where you are based on time lag of signals from space.

3. How do we show elevation? Elevation, or altitude, is height above some reference. Shading or color coding can give a sense of sloped or flat areas. Hatchures are little marks to show downslope. The main method is the use of contour lines. The shape of the land is called its topography. A topographic map uses contour lines.

4. Isolines An isoline connects all points of the same value; they form the borders on maps between areas of different ranges of values. –On a weather map, every 10 deg F band is given a color separated by isotherms. –A contour line connects all points of the same elevation. –The map will say the units and the spacing, or contour interval, between adjacent lines.

5. Rules for Contour Lines The contour interval cannot be skipped. Adjacent lines are separated by 1 C.I. or have the same direction because you are changing slope. Not all lines are labeled. USGS maps of our area use heavier brown lines for multiples of 100 feet, but show in between values every 20 feet.

6. Rules for Contour Lines, cont All contour lines close or run off the edge of the map. Contour lines cannot cross each other. Contour lines form loops around depressions or hills. Depressions may be indicated with hatchure lines. Contour lines form V’s which point uphill when they cross a stream or gully.

7. Relief Relief is the difference in elevation between the highest and lowest locations in an area. Both plains and plateaus have low relief.

8. Profiles A profile is a side view used to show relief in a way we can visualize it easily. Profiles are useful when planning roads, or visualizing how radio/TV/cell phone signals will get out. A profile can be constructed using data from a contour map. Profiles are constructed along a straight line.

9. Vertical Exaggeration The Earth really is pretty flat – to scale, it is smoother than a billiard ball. To emphasize the change in vertical elevation, profiles are often constructed with an exaggerated vertical scale compared to their horizontal scale. VA = vertical scale / horizontal scale. Be aware when VE is used – a raised relief map will say somewhere on it what the VE is.

10. What else should maps tell us? In addition to the kind of map, it should tell you; –When it was made –Who made it –What projection was used –Which way is North –Latitude and Longitude * –If elevation is shown, what is zero?

11. The Map Key A map should not be secret (unless it’s a Pirate’s Treasure Map, Yo-Ho The key gives a way to interpret symbols, distance, colors, etc. USGS maps use a uniform set of symbols and colors. There are too many to show on each map, so you learn them or consult a separate guide.