Site Analysis - Terrain, Soils, Drainage and Buildable Area

Site Analysis shows you the land before you build on it. Draw a site (or pick one you already drew) and the kit can add:

• Contours: contour lines at the interval you choose.
• Slope: a map of how steep the ground is.
• Aspect: a map of which way each slope faces.
• Cut and fill: how much earth you would dig out and bring in to make the site flat.
• Soils: how well each soil on the site suits houses, septic fields, excavations or roads (US).
• Drainage: where water flows, stands and leaves the site, and how much runs off in a storm.
• Buildable area: the ground left to build on after steep slopes, setbacks, flooding and poor soils.

Each result is added to your map as a layer, with a report card of its numbers next to the site.

Who can use it

Site Analysis is a Pro Business kit. Every signed-in account also gets 3 free analyses to try it. Each run of any tool uses one. A run that fails does not use one. The kit shows how many free analyses you have left.

A site can be up to 250 acres (about 100 hectares).

Add the kit

1. Open Maps & Data and go to the Kits tab.
2. Find Site Analysis and click Use Kit.

You can also right-click a polygon, rectangle or circle on your map and choose Analyze site. The kit opens with that shape as the site.

Choose the site

• Use selected shape: opens a list of the areas on your map. Click one, or click Select on map and then click the shape on the map.
• Draw site: click the map to outline the site, then click the first point to finish.

The chosen site shows under the buttons with its icon, name and size. If the site is over 250 acres, draw a smaller one.

Run an analysis

Pick a tab, set its options, then click Create layer. The top row of tabs is about the shape of the land (terrain); the second row is about building on it (construction).

Contours

Set the Interval, the height between lines. Close lines mean steep ground. Wide spacing means flat ground that is easier to build on. Every fifth line is darker and labeled with its elevation.

Slope

Shows how steep the ground is, in five classes:

Class	What it usually means
0 to 5°	Suits most buildings, parking and roads
5 to 10°	Buildable with some grading
10 to 15°	Needs more earthwork
15 to 30°	Usually needs special foundations; many places limit grading here
Over 30°	Steep; high risk of erosion

Choose Degrees or Percent for the legend. The panel shows the mean slope, the steepest slope, and how much of the site is in each class.

Aspect

Shows which compass direction each slope faces: north, northeast, east and so on. Near-flat ground is shown as Flat. Aspect helps with sun exposure, wind and drainage. In the northern hemisphere, south-facing slopes get the most sun.

Cut and fill

Shows how much earth you would need to dig out (cut, in red) and bring in (fill, in blue) to make the whole site flat at one elevation.

• Balanced (cut equals fill): the kit finds the elevation where the earth you dig out is the same as the earth you need. No soil has to leave or arrive, which is usually the cheapest choice.
• Custom elevation: enter the elevation you want, for example a planned floor level.

The panel shows the cut, fill and net volumes, the area of each, and the deepest cut and fill. A black grade line shows where the flat site meets the existing ground.

Soils

Rates each soil on the site from the USDA soil survey for the use you choose in Rate soils for: houses without basements, houses with basements, septic fields, shallow excavations, or local roads and streets. Each soil is colored by its rating:

Rating	What it means
Not limited	The soil suits the use well
Somewhat limited	It can work, with some extra design or cost
Very limited	Expect serious problems; special design, high cost or a different spot

The panel lists the soils with their share of the site and rating. Soil ratings cover the United States only.

Drainage

Shows how rain moves across the site:

• Flow paths in blue, thicker where more ground drains into them.
• Outlets, the points where water leaves the site, with how much of the site drains to each.
• Standing water, the low spots where water collects, colored by depth.

Enter the Storm rain (for example 50 mm or 2 in) and the Ground cover (lawn, meadow, woods, row crops, gravel, or paved and roofed). The panel shows the runoff depth and volume for that storm, worked out with the USDA curve number method from the site's soils. Outside the United States, where there is no soil survey, the kit assumes average soil.

Buildable area

Shows the ground left to build on and why the rest is left out:

• Too steep: slopes over the Steepest slope you set (15% by default).
• Setback: a strip inside the boundary, as wide as the Setback you set.
• Flood-prone or wet, and Poor soil for building: when their boxes are checked (US soil survey).

Each buildable area is outlined in green, largest first, and the panel shows the total buildable area and the largest single area.

Resolution

Slope and aspect have a Resolution option. Auto uses the best detail the elevation data has at your site. A finer setting than the data cannot add real detail; the kit tells you when that happens.

Where the results go

Everything goes into a Site Analysis folder, with a folder for each site and a folder for each run. Contours, flow paths and buildable areas are shapes you can restyle. Soils are areas colored by rating. Slope, aspect, cut and fill, standing water and building limits are image layers, locked so they stay lined up with the map. Each run also adds a report card next to the area, with the same numbers, legend and charts as the panel. It is saved with the map, so anyone who opens or shares the map sees the report without opening the kit. The numbers are also saved in each layer's description. Press undo once to remove a whole run.

Where the elevation comes from

The kit uses Scribble Maps elevation data. Across most of the United States this is USGS 3DEP lidar at 1 meter, which shows the bare ground without trees or buildings. In other places the data is coarser, often 10 to 30 meters. Every result names its source and resolution. See Terrain elevation sources and attribution for details.

Soil ratings come from the USDA NRCS soil survey (SSURGO), which Scribble Maps keeps a copy of.

Results are estimates from elevation and soil data. They are not a survey, a soil test or a drainage study. Use a licensed surveyor or engineer for construction plans.

Ask Scribble

You can also ask Scribble, the AI assistant, for example: "show 2 ft contours for this lot", "how much dirt would it take to level this site?", "can this lot take a septic field?" or "where does water drain on this site?" with your site selected.