earth science vodcast network esvn. topographic maps
TRANSCRIPT
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