Topographic Analysis Is the Foundation of Responsible Site Design
Topographic analysis - the study of existing land form and elevation - is one of the first things an architect does when receiving a new project site. Understanding the site's existing contours, slopes, drainage patterns, and high and low points informs building placement, grading design, stormwater management, and foundation strategy. The ARE PA exam tests topographic reading and analysis through site plan exhibits that require candidates to extract meaningful design information from contour maps.
Reading Contour Lines
A contour line connects all points on a site at the same elevation. Contour lines have several properties that allow design professionals to extract site information:
- Contour interval: The elevation difference between adjacent contour lines. Common intervals are 1 foot, 2 feet, 5 feet, or 10 feet depending on the scale of the map and the relief of the terrain.
- Closely spaced lines = steep slope: The closer together the lines, the steeper the terrain.
- Widely spaced lines = gentle slope: Far-apart lines indicate flat or gently sloping terrain.
- V shapes pointing uphill = valleys and drainage: Contour lines that form V shapes pointing toward higher elevations indicate stream valleys and natural drainage channels.
- V shapes pointing downhill = ridges: Contour lines forming V shapes pointing toward lower elevations indicate ridges and high points.
- Concentric closed loops = hill or depression: Closed loops indicate either a hill (spot elevation inside is higher) or a depression (spot elevation inside is lower).
Calculating Slope
Slope is expressed as a percentage: (rise / run) × 100. To calculate slope from a contour map: divide the elevation difference between two points by the horizontal distance between them (measured on the map at scale), then multiply by 100.
Example: If two points are 50 feet apart horizontally and have a 5-foot elevation difference, slope = (5/50) × 100 = 10%.
Slope categories relevant to design: 0–2% = very flat (drainage may be difficult); 2–5% = gentle, usable for most purposes; 5–15% = moderate, requires thoughtful grading; over 15% = steep, challenging for building development; over 25–30% = very steep, unstable, may require special engineering.
Drainage Patterns
Water on a site flows perpendicular to contour lines, from higher elevation to lower elevation. By reading the contours, the architect can identify: natural drainage channels (low points and valleys), high ground that divides drainage basins (watershed divides), and areas that may collect standing water (depressions, flat areas). Stormwater management regulations typically require that developed sites not increase runoff volume or peak flow rate compared to pre-development conditions.
Building Placement Relative to Topography
- Place buildings on flat or gently sloping areas to minimize grading costs.
- Orient buildings along contours (parallel to slope lines) rather than perpendicular, to reduce cut and fill.
- Avoid placing buildings in swales (natural drainage channels).
- Consider "cut and fill" balance - minimize import or export of soil by balancing excavation with fill on site.
- Place parking on gentle slopes; avoid access drives with slopes over 8–10%.
Key Exam Points
- Contour lines: closely spaced = steep; widely spaced = flat.
- V pointing uphill = valley/drainage; V pointing downhill = ridge.
- Slope = (rise / run) × 100%.
- Water flows perpendicular to contour lines, from high to low.
- Site grading should minimize cut and fill and balance earthwork on site.
Study PA on AREprep
AREprep’s PA flashcards cover every concept on this exam with spaced repetition, and the practice exams mirror the real question formats so the actual test feels familiar.