Final answer:
A brown line with small tick marks in an aerial image usually represents a contour line, indicating a hill or an earth mound within the Arlington Park Raceway.
Step-by-step explanation:
The student is inquiring about features within an aerial image of Arlington Park Raceway, specifically identifying a natural feature represented by a brown line with small tick marks.
In cartography, a brown line with small tick marks typically symbolizes a contour line, which indicates a change in elevation or the outline of a hill or a slope. Since one of the features is identified as a pond, the other feature represented by the brown line with tick marks would likely be suggesting changes in elevation, commonly observed as hills or earth mounds within man-made settings like parks or raceways.