**Lesson Plan # 3 Topography and topographical maps**

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**Aim**: How to measure height on a top topographical [mb1] map

**Vocabulary**, topography, contour lines, contour intervals, isolines, profile, gradient, fields

**Discussion: we so far have discussed the world’s parts and how to find places using the longitude-latitude system. Today we will look into a deeper aspect of measuring space and that is measuring the layout of the land. Meaning, how do we measure the area’s on earth surface which are either mountainous or in a valley. **

**Motivation**: Now lets say you are going on a hike on Chol Hamoed in Prospect Park with your little brother and you see that there are few choices to take. You are trying to decide on which trail to go on and since you have your younger brother with you need to decide which trail would be appropriate for both of you. You are given a map (handout map) and you look around at your options on the map and you choose one. Which one would you choose and why?

You will probably look for the trail that is the easiest to climb since your younger brother cannot climb a steep mountain easily. How can you choose a easy path by just looking at a map?

**Strategy**: first describe what a topographic map and a contour line is.

A Topographical map is a bird’s eye view of a landscape or an area. So for example if you go in a helicopter over camp and you look **directly **down at the landscape, then you are looking at the topography of the land.

Can you see how high a mountain is if you look at the topography alone? No since you need to be standing on its side (or **profile**) to measure height. In order to get out of this problems Cartographers (or map makers) invented a type of line called a contour line. What is a contour line?

l **Contour lines**- is a line which connects points of equal elevation. Thus we can draw a line around a mountain which has the same area and then even when looking from a bird’s eye view we can see height. These lines are also known as isolines

l Now how can we measure between two contour lines? Well we don’t but we call it a Contour** interval** which means that at this height all around a hill is the same underneath or above the Contour lines.

l If Contour lines are close by then the slope is steep if its far in between the slope is very low. When contour lines cross a river or stream they bend upward towards higher elevations which are the source of the stream.

l A **contour profile** is where a level of elevation is shown from a cross sectional view as opposed to a birds eye view in a standard topographical map. (For an example see page 18 figure 1-12)

l Now let’s say you wanted to know how much the land goes up or down over a given distance. Then you need to find out how much the land slopes up and down and then divide it by the distance between the slopes. This amount of sloping is called the Gradient.

l The gradient or slope of a given field can be determined by (1) discovering the difference between two points on a slope and then subtracting the difference between them. The distance between two points on the slope can be figured out by measuring the difference between two islolines. For ex. If one isoline says 300 and the other 100 feet what is the difference between the two isolines-200 feet. (2) then by dividing that number by the change in the distance between the two points we will get the gradient. Thus for example if the higher part of a slope is 900 and the lower number is 400 and the distance between them is 4 km then subtract the heights and you get 500 then divide that by 4 and you get 125 km which is the measure of a slope.

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**Hand out paper **with topographical map and have students view map of Prospect Park and then answer questions one to 9 in their journals

**Closing thought**: Did you know that Yidden where very big map makers going back many hundreds of years and that because of one America was found.

[mb1]See the pasuk in Devarim 1:7 which uses Topographical description to describe Eretz Yisroel as Rav Hirsch points out