Site Analysis Begins With the Topographic Map - Learning to Read It Is a Fundamental Architecture Skill
Topography - the shape of the land - is the foundation of site analysis and site design. The topographic map (or "topo") shows existing grades through contour lines, each of which connects points of equal elevation. Reading a topo accurately allows the architect to understand slopes, identify drainage patterns, locate high points and low points, determine where cut and fill will be required to create a level building pad, and identify natural features (ridges, valleys, swales) that should inform the site design. The ARE PA exam tests site analysis and grading as core planning and analysis skills because the architect leads the site design and must be able to work fluently with topographic information.
Reading Contour Lines
Contour lines that are close together indicate steep slopes - the elevation change per horizontal distance is large. Contour lines that are widely spaced indicate shallow slopes. Contour lines never cross (two different elevations cannot exist at the same location in non-overhanging terrain). V-shaped contours pointing uphill indicate a ridge (high ground extending into lower surroundings). V-shaped contours pointing downhill indicate a valley or swale (low ground extending into higher surroundings). The contour interval - the elevation difference between adjacent contour lines - is specified on every topo and varies based on the map scale and the relief of the terrain.
Slope Calculation
Slope is calculated as rise over run: slope (%) = (elevation change / horizontal distance) × 100. If two contour lines with a 2-foot contour interval are 20 feet apart horizontally (measured on the map using the scale), the slope is (2/20) × 100 = 10%. Slope affects: accessible route design (ADA requires ramps at slopes over 5% and specifies a maximum 8.33% ramp slope with no cross slope exceeding 2%); stormwater management (flatter sites drain more slowly and may require more detention infrastructure); building pad location (slopes in excess of 15-20% require significant grading to create level pad conditions); and parking lot design (maximum 5% slope in parking areas for usability and drainage).
Drainage Patterns
Water flows perpendicular to contour lines, from higher to lower elevation. Site drainage patterns are determined by topography - water flows from ridges toward valleys and swales. The high points on a site are the drainage divides (watersheds): water on one side flows one direction, water on the other side flows the other direction. On complex sites, identifying drainage divides and understanding which areas drain toward (and potentially through) the building pad is essential for stormwater management. Buildings should not be placed in natural drainage channels - water will continue to seek the path it has always taken.
Cut and Fill
Grading a site for a building pad requires moving earth - cutting (removing material from high areas) and filling (adding material to low areas) to create a level or gently sloped surface. Economical grading is balanced: the volume of cut equals the volume of fill on the site, so no material needs to be imported or exported (hauling material off-site or importing material is expensive). Site planning should seek to locate buildings and roads at grades that minimize net cut and fill while keeping cut-to-fill balance as close as possible.
Key Exam Points
- Contour lines: close = steep; widely spaced = shallow; never cross.
- V-shapes: pointing uphill = ridge; pointing downhill = valley/swale.
- Slope: rise/run × 100; ADA ramp maximum 8.33%; accessible route maximum 5% running slope.
- Drainage: perpendicular to contours; from high to low; buildings should not be in drainage channels.
- Balanced grading: cut volume = fill volume; no material import/export needed - most economical approach.
Study PA on AREprep
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