What is a topographic map? Relationship between 3D and 2D representation
What is a topographic map? Definition: a graphical representation of the earth that includes the following: • the shape of the earth’s surface using contour lines • Symbols that represent natural features such as bodies of water • Symbols that represent man-made features, such as buildings, roads, bridges, railroads, boundaries, etc.
USGS map-standard color code • Network of streams, lakes, springs =blue • Woodland features = green • Roads, buildings, railroads,powerlines = black • Urbanized areas = red
Contour lines are imaginary lines that join points of equal elevation Index contour lines are the darker brown lines with numbers on them indicating elevation above sea level Contour interval is the difference in elevation between two adjacent contour lines
Rules for contour lines What is the contour interval on this map?
General features of contour lines • Connect points of equal elevation • The closer the contour lines are to each other, the steeper the slope • Gentle slopes are depicted by widely spaced lines • Contour lines do not cross each other • When contour lines cross a creek, they form a “V”, with the tip of the “V” pointing upstream • Closed contours (circles) represent the top of hills or mountains
Topographic profiles Definition: a diagram that shows the change in elevation of the land surface along any given line; it represents the “skyline” as viewed from a distance
Creating a topographic profile • Determine the contour interval for the map you are using. • Place a strip of paper across the topographic map where you want to determine a profile of the land. Mark the strip of paper everywhere a contour line crosses it. Label the elevation on the strip at each mark. • Move the strip of paper to graph paper that has been labeled with the appropriate elevation and record the data points. • Connect the points with a smooth line. This is the profile of the land.