Florida Museum of Natural History

P a l e o n t o l o g y  R e s o u r c e s

Topographic Maps

paleo banner

Useful Tools for the Florida Fossil Hunter

by Frank R. Rupert, P.G. 149

Maps are important tools to anyone working in the field, especially in unfamiliar terrain. One of the more useful maps for the avocational and professional paleontologist alike is the topographic map. Topographic maps have many applications in Florida.

A topographic map is a map illustrating the topography or shape of the land surface. Topographic maps show the locations and form of hills, valleys, streams, and other features as well as many man-made landmarks. They illustrate the shape and elevation of surface features by the use of contour lines. Contour lines are imaginary lines (they exist on paper only) which connect points of equal elevation on the earth's surface. They provide a means of displaying three-dimensional information on a two-dimensional sheet of paper. The vertical difference in elevation between adjacent contour lines is called the contour interval.

Contour lines on topographic maps communicate details about the actual land surface through their shape and spacing:

  1. Contour lines appear closely packed together on the steep bluffs or cliffs. In the flat or gently-regions, they are widely-spaced. This is because on steep slopes elevation increases occur with greater frequency per unit of horizontal map distance and thus appear closer together.
  2. Contour lines do not intersect, cross, or branch. They may touch or coincide only on very steep slopes (and this is commonly due to the thickness of the printed contour lines - only on vertical slopes would the lines truly coincide).
  3. Contour lines form a "V" pointing upstream (or up-gradient) in stream valleys or drainage rivulets. In closely spaced stream valleys a series of "W" shapes may result; the stream valley "V"s point towards the top of the hill, the down slope-pointed "V"s are the intervening noses of higher ground between streams.
  4. The contour interval is constant on any map. Every fourth or fifth contour line is labeled with their elevation for reference; on actual topographic maps, the contour lines representing every 50 feet of elevation are commonly labeled, while those in between are not. Spot elevations are sometimes shown for specific points on the map. All elevations are relative to mean sea level, which is taken to be the "0" foot elevation contour.
  5. Wide rivers and streams are defined by parallel lines approximating their mean width; narrow streams and creeks are shown with single blue lines; coastlines and lake shores are shown with a single unlabeled line.
  6. Local man made structures, including buildings, roads, and bridges are commonly shown on the maps.

On actual topographic maps, many of the different features are delineated in color; contours lines are brown, water is blue, roads are printed in red or black, and structures are printed in black. Cities and other large areas of manmade disturbance are usually printed in either purple or gray shading. Areas of vegetation are shaded green. The maps illustrated on the following pages of this article are, by necessity, printed in black and white. Some of the inherent "readability" is therefore lost.

Topographic maps are prepared today largely from composite aerial photographs, with field checking where needed, and provide some of the most accurate local detail available. Therefore they are a useful tool for locating possible new sites, planning fossil-hunting expeditions, and as references in accurately documenting the location of known fossil sites. Topographic maps can be especially useful in locating areas where fossiliferous strata may be exposed, either naturally by stream erosion and karst activity, or by man's excavations.


Topographic Maps in Florida

The entire state of Florida has been mapped by the U.S. Geological Survey in 7.5 minute topographic quadrangles. These maps are termed seven and a half minute quadrangles because each map covers a rectangular area of land surface equal to 7.5 minutes of longitude in width (about 7.5 miles) and 7.5 minutes of latitude in height (8.5 miles). Latitude and longitude tick marks are provided along the margins of topographic maps. One thousand and thirty seven 7.5 minute quadrangles are required to cover the entire state. The actual paper quadrangle maps are about 23 inches wide by 27 inches high. This size allows a standard scale for the map of 1:24,000 (one unit of map distance in inches, feet, or millimeters, etc., equals 24,000 of the same units on the surface of the earth). The fractional scale and a bar scale of distance is part of the information printed at the bottom of the map. The direction of true north is always towards the top of the map. Magnetic north, which may be a few degrees east or west of true north, is also indicated on the map.

Earlier topographic maps, generally dating from prior to 1940, were based on 15 minute quadrangles. These covered an area equivalent to four of the 7.5 minute maps, and had a scale of 1:62,500. The larger, modern 7.5 minute maps generally provide better detail, although the older maps can often be used to document historical changes in land features or urban sprawl.

Today, each topographic quadrangle map is given a specific name, usually based on some local geographic feature (i.e., Tallahassee Quadrangle, Okeechobee NW Quadrangle, etc.). Certain of the maps, especially those in highly-populated areas, are updated every several years to show the expansion of civilization. Others in more remote locations may not have been updated since the original mapping in the 1940s. A handy index showing the locations and names of all 1,037 quadrangle maps covering the state is printed by the United States Geological Survey.

Some practical examples of topographic map usage for the fossil hunter

In some regions of Florida, topographic maps may prove extremely useful to the avocational paleontologist in search of fossiliferous exposures. They are an aid in locating mines, quarries, sinks and incised streams, all features which might expose otherwise buried fossiliferous strata. Topographic maps may also serve to document the location of sites to revisit.

A note about geology and the pitfalls of topographic maps:

It is important to remember that the local geology plays an important part in fossil occurrence. Fossiliferous strata is not always present at shallow enough depth to be intersected by surface features. There are, for instance, many areas in Florida with incised streams, roadcuts, canals, and karst features which do not cut into fossiliferous sediments. This is true for most of Florida. Successful fossil site locating requires combining a knowledge of local stratigraphy with the shape of the land surface. The ideal method would entail using a geological map to locate areas with known shallow fossiliferous strata, then overlaying the corresponding topographic maps to locate potential hunting sites.


Obtaining Topographic Maps for Your Area:

Many public and university libraries statewide have original topographic maps available as reference materials. Digital topographic maps are fast replacing hard-copy printed versions, but some retailers may still carry an inventory of the printed paper quadrangle maps. Maps for your particular area may be available at local sporting good stores, engineering or survey equipment stores, some marinas, and outdoors or trail shops.

Lists of local paper map retailers and an online map locator with download links may also be accessed at: http://store.usgs.gov/b2c_usgs/b2c/start/(xcm=r3standardpitrex_prd)/.do

Information on pricing and ordering paper maps is also available from the U.S. Geological Survey at:

USGS Information Services
Box 25286
Denver, CO, 80225
Phone: 1-888-ASK-USGS
http://ask.usgs.gov/to_order.html

Newer digital topographic quadrangles may be downloaded from the U.S. Geological Survey at the following web address:

www.usgs.gov/pubprod

Additional topographic map resources, including maps compatible with GIS applications, may be accessed through the Florida Department of Environmental Protection's Land Boundary and Information System (LABINS) topographic web page at:

http://data.labins.org/2003/MappingData/drg/drg_us_topo.cfm

Back to Paleontological Resources Main Page