Measuring Earth / Topographic Mapping

Mapping Basics Vocabulary: Contour Interval: the difference in elevation represented by each contour line on a topographic map. Contour Line: a line on a map connecting points of equal elevation. Elevation: the height of an object above sea level. Gradient: the rate of change from location to location within a field. Hachured Lines: are contour lines with ticks pointing downslope that indicate a depression on a topographic map. Isoline: a line used on a model of a field, such as a map, that connects points of equal value within that field. Profile: a side view of Earth’s surface. Topographic Map: a map which shows elevations of the surface it depicts. Formula: Gradient = Change in elevation distance

Isolines Isolines: –Lines that connect points of equal value A correctly drawn isoline will separate data points. All values that are larger than the line drawn will be on one side of it and all values that are smaller will be on the other side. Isolines follow two general patterns. They either form: –Loops –Lines (semi-parallel) at the examples! Each isoline drawn connects equal values and separates smaller numbers from bigger numbers. Label where the big and small numbers are compared to each other

Topographic Maps What is the purpose of a topographic map? –To show an area’s height (elevation) above sea level –Sea level always has an elevation of zero (0)

Contour Interval What does “contour interval “ mean? –The value between two consecutive lines What is the contour interval for: –Map (1) 5 (units) –Map (2) 5 (units) –Map (3) 5 (units) –Map (4) 5 (units)

Elevation Elevation – –The height of a location compared to sea level (sea level is always zero) What is the elevation of –Point A 520 ft –Point B 550 ft –Point Y 490 ft –Point Z 520 ft Lines closer together indicate steeper land.

Maximum / Minimum Elevation To determine the maximum possible elevation for a hill we determine what one contour line higher than what is shown would be. Then subtract one from that line’s value. –Ex: What is the maximum elevation possible for Holland Hill? There is a contour line for 560ft One line higher than that would be 570 ft Subtract: 570 ft – 1 ft The maximum value for Holland Hill is 569 ft To determine the minimum elevation for the top of hill we would add one to the highest contour line that is drawn. –Ex: What is the minimum possible elevation for the peak of Holland Hill? There is a contour line for 560 ft Add: 560 ft + 1 ft The minimum value for the peak of Holland Hill is 561 ft

Topographic Depressions A depression is: –An area of land that is lower than the surrounding area On a topographic map, depressions are marked with small inward lines: (Hachured lines) To label a depression on a map: 1.Find the value of the nearest increasing line that is not part of the depression 2.Repeat that line’s elevation on the first hachured line (the first line of the depression) 3.Any additional hachured lines inside the depression decrease with the contour interval – at the example!!!

River / Stream Direction Rivers always flow downhill –From high elevation to low elevation When a river crosses a contour line on a map, the contour line forms a “V” shape. –The “V” points upstream to where the water is coming from Ex: Look at Maple Stream on the map. –Trace the shape of the “V”s as the river crosses the contour lines. This shows where the water is coming from. –The “V”s point to the top right of the map, so the water in Maple Stream is moving towards the: southwest Double check: is this also moving downhill? YES

Topographic Profiles Topographic Profile- –The side view of an area of land. Profiles show hills, valleys, how steep/flat the land is. Steps to creating a profile from a map 1.Line a piece of scrap paper on the topographic map between the two given points. 2.Make a small mark on the scrap paper that shows where each contour line is on the map. 3.Label each of these small marks with that point’s elevation. 4.Line your scrap paper up below the profile grid. 5.Make a dot above each mark on your scrap paper at the correct elevation. 6.Connect the points. 7.If two consecutive points have the same elevation the line should curve under or over but not touch the next elevation line.

Profile practice Match the topographic map with it’s profile 1. B 2. E 3. D 4. C 5. F 6. A

Gradient What is the gradient formula? –gradient = change in field value distance What does gradient mean (in words)? –How flat or steep the land is, how quickly the elevation changes in a given distance. Example: What is the gradient between points B and D on this map? 1.gradient = change in field value distance m – 50m 2km 3. gradient = 25m/km Contour lines that are close together show land that is steep (far apart = flat land)