3.3 Notes
• Topographic Maps
• A topographic map is a map that shows the surface
features, or topography, or the Earth.
• Most topographic maps show natural and man-made
features.
• These maps are made using a combination of aerial
photographs and survey points collected in the field.
• Topographic maps show elevation, height above sea
level.
• The mean sea level is the highest and lowest tide
levels of the ocean.
• The elevation at mean sea level is 0.
• Contour lines show elevation on a topographic map.
• These lines connect points of the same elevation.
• The shape of the lines reflect the shape of the
land.
• A contour interval shows the difference in elevation
between one contour line and the next.
• The contour interval determines the elevation at
which each contour line is drawn.
• For example, if the contour interval is 10m, then
contour might be 10m, 20m, 30m, etc…
• Every fifth line, index contours, is printed bolder than
the others to make it easier to read.
• Elevations between contour lines can be estimated.
• Exact elevations are stated and generally marked
with an X.
• The relief is the difference in elevation between the
highest and lowest points of the area being
mapped.
• Contour lines spaced widely apart indicate that the
change in elevation is gradual and that the land is
relatively level.
•Contour lines that are nearly touching indicate
extremely steep terrain such as a cliff.
• Contour lines spaced close together indicate
that the change in elevation is rapid.
• Lines that bend to form a V-shape indicate a
valley, the V points toward the higher end of
the valley or upstream if a river flows through
it.
•Contour lines that form loops indicate a
hilltop.
• Contour lines that form loops with marks on
them indicate depressions (Ex. Lake), these
lines are called depression contours. The
marks point in the direction of the depression.