Introduction to mapping How do we read maps

Introduction to mapping

How do we read maps? � Maps are selective views of reality � Size of the map relative to reality (scale) � What’s on the map (symbolization) � Shape of the map (projection)

What we’ll be looking at � Scale � Area � Distance � Gradient � Grid reference � Contour lines � Map symbols � Aerial and satellite images � Topographic profiles

Contour Lines �A contour line on a map is a line that joins points of equal elevation. Contour lines can be interpreted for this landscape based on the data given. For example, below is a map with a series of spot heights (in metres) that have been measured.

Contour Lines

Contour Lines � When drawing in contour lines one must first know the designated contour interval which is the difference in elevation between two successive contour lines. Contour intervals vary from one map to another depending upon the landscape presented. For the map above, let's see what it looks like with three contour lines drawn in using a five metre contour interval.

Contour Lines

Introduction: Contour Lines: In general, note how the contour lines are sub – parallel, they never cross or touch and they never split. Notice also that every 5 th line is a heavier line. These are called index contour lines and they are emphasized on the map to make the counting of contour lines easier. For example the index contour directly above the 2000 line is 2100. (*) How can you tell? You have to find out what the contour interval is. This bit of important information is located at the bottom center of the map. (*)

Introduction: Contour Lines: Below this it also states: Dotted lines represent 10 -foot contours. (Below that it states that the data for the contour lines was bases on information obtained in 1929. )(*) Here is an image of the bottom of the map. There is a lot of information located here, but for now take a look at the area below the graphical scales. (*) Below the scales it says the contour interval is 20 feet. (*)

Introduction: Contour Lines: In this part of the map there is a contour of 1140. (*) The next “normal” contour line would be the 1160 which is 20 feet higher. Find it on the map. (*) But, this area of the map is so flat that another contour line was added. Instead of the normal 20 feet on the map it is only 10 feet different than the one above or below it. (*) This is not the normal situation on topographic maps. (*)

Introduction: Contour Lines: So, you can see that the difference in elevation from one normal contour line to the next is 20 feet. The dotted contour line is found only in the flat area of the map. (*)

Contour Lines � Complete Handout

Contour Lines

Contour Lines � 2)A line that joins points of equal elevation. � 3) Cannot be at two different elevations at the same spot on the earth’s surface. � 4) A: 180 m B: 135 m C: 65 m D: 30 m E: 5 -10 m � 5) 50 m. This quantity is known as the contour interval. � 6)Figure 3 a: 10 m Figure 3 b: 25 m

Contour Lines � 7) The difference in elevation between two successive contour lines. � 8) Greater than 30 m but less than 40 m in elevation. � 9) If it was lower than 100 m, there would be another depression contour line within the 200 m one. � 10) It is a hill or small mountain. Greater than 300 m but less than 400 m.

Contour Lines

Contour Lines