Map exercise 2_Winter 2019_JH

pdf

School

Glendale Community College *

*We aren’t endorsed by this school

Course

111

Subject

Electrical Engineering

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by EarlFly3557

Geo 111 Lab Lab 6 Student name: _________________ Lab 6: Topo maps Goals 1. Learn how contour lines are drawn based on having few measured elevations and then adding more points by applying interpolation. 2. Determine elevation of any point using the topo map of the area. 3. Learn to draw a profile (or cross-section) along a given line on topo map. 4. Learn how shape of contour lines reflect variations in slope. 5. Determine locations of valleys and ridges. 6. Become familiar with land use from looking at a topo map. 1. Topo maps Introduction Topo maps are 2-D (coordinates) representation of 3-D data (coordinates + elevation). Contouring is a technique that is used to reduce many data points to easily understood maps. The foundation of the contour map is a contour line. You need to know at least three items to draw a contour map: 1. Data points: these are points on a map showing variation of elevation; could be bench mark elevation 2. Units of elevation: feet, meter 3. Contour line: Lines of equal elevation 4. Contour interval (C.I.): difference in elevation between two succeeding contour lines 2. Interpolation Interpolation is a method of constructing new data points within the range of a discrete set of known data points. The initial information in all contour maps is a series of data points (such as Map B in Lab-5). Although a skilled person can estimate position of the contour lines visually but for a more precise job we want to add more data points to this map and that can be done by interpolating between points as the following exercise teaches you. Question 1. Map B in lab-5 exercise included many data points such that you could easily draw the contour lines. Now we want to work on a relatively harder example. In the map below, data points are elevation above sea level. For adding more elevation points do the following: a) Using a ruler divide the distance between all data points into equal divisions based on the contour interval. For example, if the value of one point is 38 and the value of the adjacent is 51, and the contour interval is 5, then the following contours pass between these two points: 40, 45 and 50. Note that contour line values should be whole number multiples of 5 m. b) Ideally you would need dividing the distance between all points in the map before beginning to draw your contours. You do as many as you can considering the lab time and time required for doing other questions. c) In dividing the distance between points, you need to be as precise as possible. Use a ruler and a calculator to make sure divisions between points are equal. Draw straight lines connecting points.

Geo 111 Lab Lab 6 Note that elevation of the benchmarks have been determined by surveying and provides the basis for drawing contour lines by interpolation (see below). Maps like this are used in construction, geological and mining projects.

Geo 111 Lab Lab 6 Interpolation instructions : As the figure above guides you, use a ruler and connect points 38 and 51 as an example. Measure the length of the line you draw. Divide that length by elevation difference which is 13 m: 54 mm / 13 m = 4.2 mm/m. Then 4.2 mm downhill from 51 mark the new point with elevation of 50 m. Using the same method, 21 mm (4.2 x 5) downhill from 50 is point 45. And, another 21 mm downhill from 45 is point 40. See, you have readily added 3 new points to your map. After adding enough elevation points draw the contour lines with C.I. = 5 meters. Rules for Contouring ● Contour Lines connect points of the same value. In topographic maps that would be elevation. ● Contour Lines do not cross or intersect each other. ● Consecutive contours lines increase or decrease by the amount of the Contour Interval. ● Contour Line va lues increase or decrease systematically with no missing intervals. ● Evenly -spaced contours suggests uniform rate of change (e.g. topographic slope). ● Closely -spaced contour lines indicate steep rate of change. ● Widely -spaced contour lines indicate gentle elevation gradient.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Geo 111 Lab Lab 6 1. Topographic profile Below is a picture showing how the contour lines translate into shape of the land surface. The top drawing shows contours, the bottom drawing shows a profile (or cross section) of the land (hills and valleys) along line A- A’ . Note how the two drawings relate. Question 2. Learn how the profile is drawn from the top topo map. Learn tools and techniques used for constructing a topo profile. a) What is C.I.? Hint: check the map margin. b) With a pencil write down elevation of each contour where it is crossed by line A- A’. c) On Y-axis of the bottom grid (representing a graph paper) mark elevation of all crossed contours. d) Using a ruler draw a vertical line from each point crossed along A- A’ on the top map to the corresponding elevation on the bottom graph. Put a cross (X) where the vertical line intersects the matching elevation line. e) Connects those points. f) Explain the result.

Geo 111 Lab Lab 6 Question 3. Create a topo profile along X-Y. a) What is C.I.? Hint: check the map margin. b) With a pencil write down elevation of each contour where it is crossed by line X-Y. c) Draw a grid at the space provided above, and mark the Y-axis with elevations. d) Draw the profile. e) How do the contours behave at the canyon bottom?