This is a description of a project in which an elevation profile (topographic profile) of Virginia was constructed along a transect line from the Atlantic Ocean to the western edge of the state along the Kentucky border. We are detailing the steps in the construction of the profile to encourage geography students to create their own profiles. Then we will analyze the profile and discuss how it relates to Virginia's physical geography.
This article was first published in the Virginia Geographer (Fall-Winter, 1991 issue).
When the project was in its planning stage, the first consideration was where the topographic profile should be placed. The aim was to include as many well-known landmarks as possible while giving a reasonably accurate representation of the topography of the state. A line oriented roughly east-west was preferred as it would cut across the greatest variety of physiographic regions. It would also follow the natural shape of the state and correspond with the reader's inclination to view a profile oriented with east on the right.
A more than suitable line was found that ran from Metompkin Island, off Accomack County on the east, to Appalachia, near Big Stone Gap in Wise County on the Kentucky border. The advantage of this line is that it intersects the cities of Richmond, Lynchburg, Bedford, Roanoke, Salem, and Norton and the towns of Appomattox and Blacksburg.
The next consideration was the vertical exaggeration of the profile. Like relief globes, the kind of vertical relief shown here greatly over-emphasizes the topography; in this case, by a factor of 21. The vertical relief is exaggerated 21 times; that is, points appear 21 times higher than they would actually be in such a cross section. This is necessary to show any vertical dimension at all, because even on a map as large as the Virginia road map issued by the Department of Transportation, the height of the state's tallest mountain, Mt. Rogers, would be only one-twelfth of an inch tall if accurately represented in cross section.
It was decided, after some trial and error, to construct the profile on sheets of graph paper measuring .1 inch by .1 inch. Thus, on the profile one square equals two miles horizontally, and the same square equals approximately 500 feet vertically. Vertical exaggeration is defined as the vertical distance of a unit of measurement divided by the horizontal distance of the same unit of measurement. By the standard we adopted one inch equals 5000 feet vertically and 20 miles horizontally.
The line was then drawn on a standard USGS topographic map of the state at a scale of 1:500,000 and on the corresponding pages in the 1989 DeLorme Virginia Atlas and Gazetteer at a scale of 1:150,000. The USGS map with contour elevation lines every 200 feet was used to glean a more general idea of the topography. The Atlas afforded a much more detailed topographic view but with a contour interval of 40 meters. Thus, when the topography was simple enough to allow it, as on the relatively flat Coastal Plain, the small-scale USGS map was easier to work with.
Coastal Plain transect
Where the topography became more complicated, as in the Ridge and Valley region, a larger scale was easier to use. The two maps had not only different contour intervals but the contour intervals of the USGS map were in feet and those of the Atlas in meters. Where the topography was extremely complicated standard USGS topographic sheets at a scale of 1:24,000 were consulted. Some calculation was needed, on occasion, to register the two contour intervals to each other.
Using 8 1/2 by 11 inch graph paper with ten squares to the inch, it took four sheets to complete the entire profile. It is interesting to note that even with a horizontal distance that took four sheets to cover, only about 1 and 1/8th inches were needed to cover the vertical distance. Beginning in the west and working towards the east, horizontal points (locations) were matched with their vertical counter parts (elevations) and connected with straight lines. A certain amount of artistic license was then used to smooth the line to give it a more curved, natural look. Interpolation was used to estimate peaks and valley floors.
The most time consuming part of the profile was in the Ridge and Valley section--again due to the extremes in elevation. This section needed careful checking against whatever benchmarks and reference landmarks were available. Having to convert from meters in the Atlas to feet on the profile was, as stated, a tedious task. An easier part was the Coastal Plain section, where several inches horizontal distance in the Atlas might cross only one contour interval.
While this particular line selected for the cross section has the advantage of intersecting a number of major Virginia cities, it happens to cross the Blue Ridge at a relatively low elevation, only about 2100 feet. Therefore, the profile of Mt. Rogers 100 miles to the southwest, was sketched in dashed lines for comparison. The placement of Mt. Rogers was determined by a perpendicular to the topographic profile line.
Ridge and Valley and Appalachian Plateau transect
The four sheets, when complete, were reduced by photocopier until the horizontal line was about twenty inches long. At this point it was decided that the profile could be shown best on a single standard size page by dividing the line into three segments rather than reducing it further. Thus, decisions had to be made concerning where to break the line. It happened that breaks were possible at the Montgomery County-Roanoke County line and the Chesterfield County-Richmond City line that made the resulting three segments similar in length, but with the eastern segment slightly shorter than the other two.
Vertical lines were drawn from the sea-level line to the profile line to indicate county and city boundaries. In certain instances the area in a political unit was very small, and some time was spent finding ways to fit all the names. As luck would have it, the smallest units tended to have the longest names! A particularly difficult problem was encountered where the line crossed Roanoke County, then the City of Salem, then Roanoke County again, then the City of Roanoke, and finally Roanoke County once more.
Transect through Roanoke County (and Blue Ridge/Piedmont provinces)
Political or cultural features were labeled along the horizontal sea-level line, while physical features, more related to the topography, were placed along the topographic line. Distinctive peaks, rivers, and other important physical geographical points were included, along with major cities, towns and highways. In addition tick marks were placed below the sea-level line to indicate approximate boundaries of the regions indicated. Finally an inset map was included with the transect line shown as a reference aid. The penciled compilation map was overlaid with drafting film and inked-in using a single rapidograph #0 pen. Type was produced on a digital Kroy lettering machine and affixed to the drafting film.
Essentially, Virginia's regions are part of much larger physical regions that in many cases extend the length of the East Coast. The elevation profile shows how low the Coastal Plain lies above the ocean and rivers. The Piedmont is higher, but still relatively lowlying until the western edge of the Piedmont along the Blue Ridge is reached. West of the Blue Ridge a number of peaks of the Ridge and Valley region are crossed. The profile follows the Ridge and Valley region for a considerable distance from Russell County to the Blue Ridge east of Roanoke.
The Great Valley is that portion between Fort Lewis Mountain and the Blue Ridge. Interstate 81 runs through the Valley but not at all along its floor; rather it hugs the ridge at an elevation of about 350 feet above the City of Roanoke in the Valley floor. Finally the higher Cumberland Plateau is reached, up to about 3000 feet in elevation.
Virginia is unusual among Eastern states in having such diversity of topographic regions. For example, Abingdon in Washington County is located in the Ridge and Valley region 25 miles from the Appalachian Plateau and the Blue Ridge, and less than 100 miles from the Piedmont. Similarly, Northern Virginia straddles the Coastal Plain, Piedmont and Triassic Lowland and is less than 25 miles from the Blue Ridge and Great Valley. Such diversity within small areas is uncommon in most regions of the country.
In broad outline the topography of Virginia east of the Blue Ridge is simple; the flat Coastal Plain and the rolling Piedmont "tilt" to the southeast. This is evident from the pattern of all the major rivers: the Potomac, Rappahannock, York, James, Nottoway, Meherrin, Roanoke and Dan. West of the Blue Ridge the pattern is much more complex because, starting in the north, the Valley first "tilts" northward as evidenced by the northeast-flowing Shenandoah.
Then a divide near the Augusta-Rockbridge county line separates the headwaters of the Shenandoah from the south-flowing tributaries of the James (the Jackson, Maury, and Cowpasture Rivers). Farther south, the New River flows northwestward into West Virginia and the Ohio River. Finally, in Southwest Virginia the Valley slopes south again as indicated by the various forks of the Holston which flow southwestward to the Tennessee River.
Three of these drainage areas are shown on the elevation profile. The first is indicated by Sandy Ridge near the junction of the boundaries of Dickenson, Wise and Russell counties. It is marked on the elevation profile as the Tennessee Valley Divide because it separates that river's drainage from drainage of the Ohio River. Ohio River system drainage does not show on the elevation profile at this point, however, because those rivers flow north from Sandy Ridge and are not intersected by the profile. On the profile, rivers to the west of Sandy Ridge drain into the Powell; rivers to the east drain into the Clinch; both then feed into the Tennessee. Rich Mountain in Tazewell County is the next major divide. It separates tributaries of the Clinch from those of the New River. Rich Mountain is also the highest point along the elevation profile, approximately 3540 feet.
Less than half a mile south of the line of the profile, Rich Mountain reaches its highest elevation at 4270 feet. Tributaries of the New River lie to the east of Rich Mountain until the New River itself is reached at the Pulaski-Montgomery County boundary. At Blacksburg near the small Virginia Tech Airport, lies the divide between tributaries of the New River and tributaries of the Roanoke River. The next divide is near the Bedford County-Lynchburg City line which separates tributaries of the Roanoke River from those of the James. Most remaining rivers are part of the James drainage system until east of Richmond, the Pamunkey, Mattaponi and Rappahannock are crossed. Then Eastern Shore drainage is reached where small rivers flow either into the Chesapeake or the Atlantic.
As students draw their own elevation profiles, an important consideration is to select a route with diversity in elevation. Any profile that crosses only the Coastal Plain and Piedmont will be relatively uninteresting. Some students may wish to construct a profile along a road. For example a profile could be made of Route 58 across the southern edge of the state, or Route 60 from Covington to Hampton Roads. If this is done the student should remember that the profile no longer reflects a straight line although it may be portrayed as such.
If a student chooses a road to profile it is best to avoid interstate highways because so much of the landscape along these routes has been artificially added or removed to make the road as level as possible. Similarly a profile along the course of a river will show less dramatic changes in elevation because of the natural downcutting and infilling of water action. A profile of the Appalachian Trial would show little change in topography because so much of it is at high elevation.
One handy source of information that may be of help to students in selecting a profile is the Department of Transportation's road map of Virginia which gives elevations of major peaks and passes where roads cut across the Blue Ridge. A second source, the Virginia Statistical Abstract, published by the Center for Public Service at the University of Virginia, gives the elevations of the fifty highest mountains in Virginia.