To navigate terrain using a map, understanding how two-dimensional lines represent three-dimensional landforms is necessary. Topographic maps use contour lines, which are imaginary lines connecting points of equal elevation above sea level. These lines allow users to visualize the slopes and features of the land. Among the many terrain features represented, the “draw” is a common, smaller landform requiring specific knowledge to identify.
Defining the Draw Feature
A draw is a natural landform described as a shallow, usually dry, drainage course found on the side of a larger hill or mountain. It is essentially a depression that is less developed and smaller in scale than a full valley or canyon. The primary function of a draw is to collect and funnel water runoff from the higher ground during precipitation.
Unlike a valley, which may contain level ground, a draw generally lacks any flat terrain within its confines. The ground slopes upward in three directions and downward only toward the foot of the slope. Draws are often carved out by water flow and may contain an ephemeral stream or loose rocks from erosion. They are typically oriented perpendicular to the main ridgeline, rising and disappearing into the adjacent slope.
Reading the Contour Pattern
The definitive characteristic of a draw on a topographic map is the specific pattern formed by the contour lines. These lines will bend into a distinct “V” or sometimes a “U” shape as they cross the feature. This concave pattern indicates a re-entrant, or an indentation, in the side of the slope.
Interpreting the direction of the draw requires applying the fundamental principle known as the “Rule of V’s”. This rule states that the point, or closed end, of the V-shape always points toward the higher elevation, which is upstream or uphill. Conversely, the open end of the V always faces downhill, pointing in the direction of water flow.
The spacing of these V-shaped lines also provides information about the steepness of the draw. When the contour lines are tightly packed together, it signifies a steep slope within the draw. If the lines are widely spaced, the draw is much gentler and easier to traverse.
How a Draw Differs from a Ridge
A draw is often considered the inverse of a ridge or a spur, which are projecting lines of high ground. While both features are represented by V- or U-shaped contour patterns, the direction the V points is the crucial difference. On a ridge, the V-shape points toward lower elevation, or downhill.
This distinction is important for navigation and movement across the landscape. Since the V for a draw points uphill, a hiker crossing it must descend to the bottom and then immediately ascend the other side. Conversely, the V for a ridge points downhill, indicating a climb to a high point.
A ridge or spur represents ground that slopes downward in three directions and upward in only one, which is the opposite of a draw. Recognizing this reversal in the contour pattern is necessary for accurately identifying whether the feature is a low-lying drainage route or an elevated line of ground. Correctly applying the Rule of V’s allows for precise terrain visualization and safer route planning.