Earth Science Vodcast Network

ESVN

Topographic Maps

Topographic or Contour Maps

• Show surface features of the Earth

- natural or man made• Topography- size and shape of land• Show elevation

-height above sea level• A top or aerial view

How is elevation shown on topographic maps?

• Contour lines are drawn connecting areas of equal elevation (isograms)

• Shape reveals land features

• Contour interval is the distance between contour lines

Contour Lines cont.

• Spacing of lines depends on RELIEF- the difference between the highest and

lowest points

• Every 5 th line is made in bold print & is called an INDEX CONTOUR

How do I interpret spacing on a contour map ?

• Closely space lines mean the land is steep

• Widely spaced lines mean the land is flatter or more gently sloping

Valleys, Streams & Mountain Tops

• Contour lines make V’s when they form valleys or cross streams

• The V points uphill or upstream

• A closed loop or circle represents a mountaintop or ridge

How do contour lines show decreases in elevation?

• Contour lines drawn with short , perpendicular lines are called HACHURES

• They represent decreasing elevation

• The first hachure is equal in elevation to the closest regular contour line

• The next hachure represents a decrease in elevation equal to the contour interval

What do the following colors mean on a topographic map? See p 876

• Blue- water• Brown- contour line

• Green- vegetation

• Red- highways

• Black- constructed features

What is a Bench Mark?

• An exactly measured elevation

• ▲ followed by a number marks the spot

U.S.G.S. Maps-Quadrangles

15 minute

• 15’ lat/longitude• 13 X 17.5 miles• 1: 62 500• 1 inch on map equals 1 mile• ____ area• ____detail

7.5 minute

• 7.5’ lat/long• 6.5 X 8.75 miles• 1: 24 000• One inch on the map equals 2000 feet • ____area• ____detail

U.S.G.S. Maps-Quadrangles

15 minute

• 15’ lat/longitude• 13 X 17.5 miles• 1: 62 500• 1 inch on map equals 1 mile• _more_ area• _less detail

7.5 minute

• 7.5’ lat/long• 6.5 X 8.75 miles• 1: 24 000• One inch on the map equals 2000 feet • _less_ area• _more _detail