Mapping: Topo and Contour Maps

1. Mapping:Topo and Contour Maps

2. O.K. ~ • Now that we’re experts on latitude and longitude; how can we use them? • We use latitude and longitude as a basis to create and read maps.

3. Maps come in many shapes and sizes . . . • Globes – Round maps • Highway Maps – flat, no geologic features • Topograhic Maps – Shows landforms on a flat surface through the use of contour lines.

4. Contour Maps/Topo Maps • A Contour Map is a topographic map that represents Earth’s surface features through the use of isolines – lines that connect points of equal elevation. • Topography : Surface features of an area (both natural and man-made) • Topo maps are flat maps that use contour lines and symbols to represent land features.

5. A topo (topographic) map is a map that shows elevation. It’s THE map to bring when going wilderness hiking. • **Contour lines show elevation above or below sea level. • **Contour Interval is the amount of elevation change between contour lines. • ** Contour lines will never intersect because they represent different elevations; there cannot be two elevations at any given point.

6. Contour lines and streams: • **When a contour line crosses a stream, it always points upstream. [This makes sense, because a streambed is at a lower elevation than the land it crosses. Therefore, the contour line must travel upstream to find a point of equal elevation in the stream’s bed.]

7. Rules of contour lines: • **The closer together the contour lines the steeper the slope; the farther apart they are, the more gentle the slope. • Contour lines (or any other isolines for that matter) don't cross or branch with another contour line, ever. • Where contour lines make a bull's eye (a series of concentric circles), there is a hill top. -- Unless there is a benchmark [] or an [x], indicating the actual elevation of a hill, you cannot determine the exact elevation of the hill’s highest point from the contour lines.

8. More on contour lines . . . • When a contour line crosses a stream/river, it makes a ‘V’. The point of the V always points the opposite way a stream is flowing. **So, we can determine the direction a stream is flowing by noting the direction the contour lines are pointing. • Hachured Contour lines occur when there is a negative change in elevation which indicates a depression or valley.

9. Calculating the Gradient of a slope: • The slope or gradient is the rate of change from place to place. • You can estimate the gradient by observing the isolines • Close together = steep gradient [cliff, mountain] Far apart = gentle gradient [field, plain] GENTLE STEEP

10. The formula is as follows: (difference in elevation between two points) Change in field value Distance (How far apart the points are, usually miles) • The units for gradient are feet/mile OR m/km

11. A profile is a side view of a hill or valley.

12. Rules for drawing profiles: • Draw/find a straight line through a landform with a point at both ends. • Put a blank piece of paper along that line from point to point and mark off the starting and ending points and every point that a contour line crosses. • Using your now plotted paper, place it on the x-axis of a graph where the y-axis is scaled using the contour interval given to you on the map.

13. More rules . . . • Mark the elevations directly above each mark you made in step #2 using a point. • Connect the points with a fluid line to show a side view of the landform. • Voila! You have a map profile!

14. So, in conclusion to our Contour Lines (hint, hint) • In order to draw a topo/contour map, we need to have the following data: • Accurate measurement of latitude/longitude • A plethora of elevation points • contour/isolines connecting those points