Topographic Maps and Coal Reserve Study
Topographic Maps
Simplest definition of a MAP: A map is a 2-D representation of 3-D surface.
A topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features.
There are several rules to note when viewing topographic maps:
- The rule of V’s: sharp-pointed vees usually are in stream valleys, with the drainage channel passing through the point of the vee, with the vee pointing upstream. This is a consequence of erosion.
- The rule of O’s: closed loops are normally uphill on the inside and downhill on the outside, and the innermost loop is the highest area. If a loop instead represents a depression, some maps note this by short lines radiating from the inside of the loop, called “hachures”.
- Spacing of contours: close contours indicate a steep slope; distant contours a shallow slope. Two or more contour lines merging indicates a cliff.
Totographic maps are of vital inportance for any kind of geological studies. In coal geological investigations, topographic maps are extremely useful in many ways such as:
- Identifying and map old strip benches: Contour strip in mountains are often easily identifiable by flat nature of contours that usually runs somewhat at a certain elevation. While we prepare reserve maps and calculate tonnage, it is very important to assign depletion polygons to the old strip mined areas and adjust our seam outcrop to the edge of the present high-wall. In many cases, the outcrops are generates using borehole data with a different softwares (example: SurfCAD). Surfcad can not identify the old strip benches unless a geologist assign depletion due to old stripping.
- Draw outcrop: To draw the proper outcrop, we produce structure map first and then choose points of equal seam elevation and surface elevation to prepare the proper outcrop of the seam.
- Identify Drainage: Rivers and creeks are easily identifiable in topographic maps.
- Identify Major Features: Identify buildings, roads, ponds, gas lines etc (if they are shown on the map).
Totographic Maps in the United states
The United States Geological Survey (or USGS), a civilian Federal agency, produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest (both in terms of scale and quantity) and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale virtually unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, and areas of Alaska near Anchorage, Fairbanks, and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles (166 km²). At 49° north latitude, 49 square miles (127 km²) are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale naturally requires a separate and specialized romer scale for plotting map positions. In recent years, budget constraints have forced the USGS to rely on donations of time by civilian volunteers in an attempt to update its 7.5-minute topographic map series, and USGS stated outright in 2000 that the program was to be phased out in favor of their National Map (not to be confused with the National Atlas of the United States produced by the Department of the Interior, one of whose bureaus is USGS).
An older series of maps, the 15-minute series, was once used to map the contiguous 48 states at a scale of 1:62,500, but was discontinued some time ago for maps covering the continental U.S. Each map was bounded by two parallels and two meridians spaced 15 minutes apart – the same area covered by four maps in the 7.5-minute series. The 15-minute series, at a scale of 1:63,360 (one inch representing one mile), remains the primary topographic quadrangle for the state of Alaska (and only for that particular state). Nearly 3,000 maps cover 97% of the state. The U.S.A. remains virtually the only developed country in the world without a standardized civilian topographic map series in the standard 1:25,000 or 1:50,000 metric scales, making coordination difficult in border regions (the U.S. military does issue 1:50,000 scale topo maps of the continental U.S., though only for use by members of its defense forces).
The next-smallest topographic series, in terms of scale, is the 1:100,000 series. These maps are bounded by two lines of longitude and two lines of latitude. However, in this series, the lines of latitude are spaced 30 minutes apart and the lines of longitude are spaced 60 minutes, which is the source of another name for these maps; the 30 x 60-minute quadrangle series. Each of these quadrangles covers the area contained within 32 maps in the 7.5-minute series. The 1:100,000 scale series is unusual in that it employs the Metric system primarily. One centimeter on the map represents one kilometer of distance on the ground. Contour intervals, spot elevations, and horizontal distances are also specified in meters.
The final regular quadrangle series produced by the USGS is the 1:250,000 scale topographic series. Each of these quadrangles in the conterminous United States measures 1 degree of latitude by 2 degrees of longitude. This series was produced by the U.S. Army Map Service in the 1950s, prior to the maps in the larger-scale series, and consists of 489 sheets, each covering an area ranging from 8,218 square miles (21,285 km²) at 30° north to 6,222 square miles (16,115 km²) at 49° north. Hawaii is mapped at this scale in quadrangles measuring 1° by 1°.
USGS topographic quadrangle maps are marked with grid lines and tics around the map collar which make it possible to identify locations on the map by several methods, including the graticule measurements of longitude and latitude, the township and section method within the Public Land Survey System, and cartesian coordinates in both the State Plane Coordinate System and the Universal Transverse Mercator coordinate system.
Other specialty maps have been produced by the USGS at a variety of scales. These include county maps, maps of special interest areas, such as the national parks, and areas of scientific interest.
A number of Internet sites have made these maps available on the web for affordable commercial and professional use. Because works of the U.S. Government are in the public domain, it is also possible to find many of these maps for free at various locations on the Internet. Georeferenced map images are available from the USGS as digital raster graphics (DRGs), in addition to digital data sets based on USGS maps (notably Digital Line Graphs (DLGs) and digital elevation models (DEMs)).
National Map: National map is interactive map service that you can access online to obtain geographic information. VIEW US MAPS ONLINE.
If you are searching for map at a particular quad, use this link: http://www.ngs.noaa.gov/cgi-bin/ds_quads.prl
Recommended Tool:
It is often useful to use Google Earth and Google Maps too. Special for a field trip project. Google Software Pack is a bundle of great FREE softwares that you can download including “Google Earth”. Very useful and handy to check great aerial topo not only in the US but all over the world.
You can use the link below to obtain GOOGLE SOFTWARE PACK.
Google Maps are also handy and you can turn on the “Satellite View” to clearly see features like mountains, tree covers, reliefs, and so on. Here is a satellite enables google map for West Virginia, USA
View Larger Map
Parts of the article has been taken from WIKI
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2 Responses to “Topographic Maps and Coal Reserve Study”
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Here’s another source for you…
National Geographic Maps has just announced an agreement to provide Nat Geo’s TOPO! maps and i-cubed’s domestic aerial imagery through i-cubed’s DataDoors imagery services — signaling an important fusion of high-quality topographic maps with one of the world’s most comprehensive and efficient delivery systems. By way of the Nat Geo DataDoors portal (www.natgeodatadoors.com), customers can select the exact area of coverage they want and quickly get the maps and imagery they need in the format they want.
More information can also be found here: http://www.gisuser.com/content/view/14210/
-Cindy, NG Maps
Thanks for the update Cindy. Much appreciated.