Above or below sea level topography (topo) maps depict in detail the surface level shapes and features of an area. Although topo maps show basic map features, such as longitude and latitude data and scale referencing, they also use color, lines and other symbols to represent vegetation, waterways and/or manmade structures. In addition, they utilize contour lines---lines that connect spots on the map of equal elevation---to represent 3D shapes, show changing elevation and the height of surface areas. Once you relate the map depictions to their respective landmarks, you can easily read and use a topo map.
Instructions
1. Review your map key to determine the meaning of each color on your map. A color can directly match the real feature it depicts (blue for water or green for vegetation) or not (gray or pink for manmade structures) depending on the cartography standards used at the time the map was made and the purpose of that specific topo map.
2. Look at shades of color and patterns overlapping colors as shades/patterns represent additional details. For example, wavy lines on a river can represent rapids or a dark blue pattern can represent a flood zone.
3. Compare line types, colors and widths on your map to the key, as lines provide additional detail. Straight, solid, dotted, dashed and curved lines, and/or a mix of line types, can represent important features such as primary or secondary roads, power lines, railroad tracks, waterways, boundaries and land contours. A solid blue line can run through several colored areas to represent a stream or a solid blue line outlining a solid white area can represent a lake or pond that appears only when it rains.
4. Go to the "Contours" section of your key. Contours appear as curved solid, dotted or dashed lines of varying widths and colors that meet yet do not cross other lines. Wide or dark lines marked by numbers, called index contours, appear at evenly spaced intervals to represent a reference elevation point. Thin contour lines, called intermediate or supplementary contours, appear between index contours to represent a change in land slope---lines close together show steep slopes and lines widely spaced apart show less or no slope.
5. Extract the "contour interval," the amount of elevation between contour lines, from the margin or your map. Contour intervals typically appear as rounded evenly divided numbers from 10 to 100 feet (10, 20, 30... or 100, 200, 300...), with flat areas represented with numbers below 10 feet. For example, a map has intermediate contour lines closely spaced below an index contour marked 600 feet and a contour interval of 20 feet. The first line below that index reference equals a steep sloped area at 580 feet of elevation.
6. Use basic mathematics to determine the contour interval between one index contour and another instead of using the contour interval key. Take two index contours, subtract the smaller index contour number from the larger to determine the difference in elevation from one to the other, count the number of intermediate or supplementary contour lines between the two and divide the difference in elevation by the number of lines.
Tags: contour interval, contour lines, index contour, index contours, between index, blue line, difference elevation