TOPOGRAPHICAL MAPS

Map Scales

A map scale is the ratio of the distance on the map to the distance on the earth

Eg. 1 : 100 000 map on land

This ratio can be shown in 3 ways:

• Verbally (1 cm equals 50 km)

• Graphically (see next page)

• Numerically (1/1000 or 1:100 000)

• Maps are much smaller than the pieces of land they represent.

• The more closely the map approaches the land in size, the larger it’s scale is.

Eg. 1:1 000 is a large scale map

1:1 000 000 is a small scale map

• Sometimes conversion factors are necessary to convert into practical units

Eg. How many km would 1 cm represent on a map with a scale of 1:200 000?

(1 km=1000 m & 1m=100 cm, so 1 km=100 000 cm)

200 000cm = 2 km, so 1cm on the map equals 2km

(other conversions: 1 mi=5280 ft &1 ft=12 in)

Contours

• In order to show landforms, maps must show the relief (highs and lows) of the land

• Topographical maps show relief using contour lines, which are drawn to connect points at the same elevation

• Contour maps are made by surveying the land to find the elevations of different areas

• A contour interval is the difference in elevation between two consecutive contour lines (it is varies with the relief of the land)

What is the contour

Interval on this map?

(in meters)

• When contour lines are close, the slope is steep• When contour lines are far apart, the slope is

gentle• To make reading the contour lines easier, every

fifth line is made darker and its elevation is marked

• The contour interval is always marked at the bottom of the map

• Contour lines show the elevation of the land, the steepness of its slopes and the shape of the land at various heights

Depression Contours

• Depression contours are drawn to show an area that is lower

• It is drawn like a contour line but marked on the inside

• The first depression contour is read at the same elevation of the ordinary contour around it, and each depression contour is lower than the one before it (uses the same contour interval)

Bench Marks & Spot Elevations

• A bench mark is a location whose exact elevation is know and notes on a brass or aluminum plate and permanently set into the ground

• Spot elevations are elevations of points of special interest

Reading a Contour Map

• Contour maps will show direction (true north and magnetic north, shown by the magnetic declination symbol)

• A map scale is also shown (using one of the three ways, usually graphically)

• Ridges are shown as long oval lines and hills are shown as a series of enclosed circles

• A river valley is obvious, because the contour lines curve in the direction of higher land (upstream)

Average Slope

• The average slope or gradient between any two points on a contour map can be determined.

Average slope=change in elevation (ft or m)

distance (mi or km)

Contour Map Profiles

• A profile shows the ups and downs (elevation changes) of a section of land between two points

*We will learn how to do this, but this is what it looks like!