Topographic maps transform a three-dimensional landscape into a flat, two-dimensional representation using contour lines to illustrate the shape and elevation of the land. This allows users to visualize terrain features like hills, valleys, and slopes. A common feature on these maps is the draw, which provides specific details about local drainage and topography. Identifying this minor feature is fundamental to successful map reading and backcountry travel.
Defining the Topographic Draw
A draw is a minor terrain feature defined as a shallow, V-shaped depression that descends the side of a hill or mountain. It is essentially a less developed stream course than a full valley, often found along a ridge side. The ground within a draw slopes downward in one direction and upward in the other three, meaning there is typically little level ground within its confines.
A draw acts as a natural drainage channel, funneling water runoff from higher elevations. While generally dry, draws may contain an ephemeral stream or loose rocks from erosion, especially following heavy rain or snowmelt. In land navigation, a draw is sometimes referred to as a re-entrant, highlighting its nature as an indentation into the slope.
Identifying the Draw Using Contour Lines
Contour lines depict a draw on a topographic map using a distinct V- or U-shaped pattern. The closed end of the V or U shape always points uphill, toward higher elevation. This upward-pointing V indicates the bottom, or lowest point, of the terrain feature. To confirm the direction of higher elevation, a map reader must examine the labeled index contours or use the map’s contour interval.
The spacing between the contour lines indicates the steepness of the draw’s sides. Closely packed lines signify steep terrain where vertical elevation changes rapidly. If the lines are spaced farther apart, the slope is more gradual. A draw’s V shape may appear more rounded, or U-shaped, if the sides of the depression are less steep.
Distinguishing Draws from Spurs and Valleys
Draws are often confused with other terrain features that also use V- or U-shaped contour lines, particularly the spur and the valley. The difference between a draw and a spur is determined by the direction the “V” points on the map. A spur is a sloping line of high ground projecting from a ridge, and its contour lines form a V-shape that points downhill, away from higher elevation. In contrast, the draw, being an indentation, always points its V-shape uphill.
Distinguishing a draw from a valley relies primarily on scale and development. A valley is a large, low-lying area between higher ground, often containing a permanently flowing river or stream. While a draw is similar to a valley on a smaller scale, it is typically shallower, less developed, and lacks the level ground necessary for easy movement. A draw tends to be perpendicular to the main ridgeline, rising until it disappears up-slope, whereas a valley is a more significant, long-term feature.
Practical Uses for Navigation
Understanding the location of draws is helpful for route planning and land navigation. Draws often represent a path of less resistance when ascending or descending a steep slope. However, caution is necessary, as funneled water flow can make the surface rocky, slippery, or prone to flash flooding. Draws also accumulate water, making them a potential, temporary source following precipitation.
For navigators, draws serve as useful linear features for a technique called “hand-railing.” This involves following the distinct edge of the feature to guide the traveler toward a specific destination. Using the draw as a constant reference point helps a hiker maintain a bearing and minimize disorientation in difficult terrain.