Slope Map Generator: See How Steep the Land Is, Anywhere

What a Slope Map Shows

Slope is how fast the ground rises or falls: the height change divided by the horizontal distance. A slope map gives every small part of the land a colour for its slope class, so you see at a glance where the flat land is, where the gentle slopes are, and where the ground is too steep for a house, a road, a tractor or solar panels. A contour map shows the same thing with lines that you have to read; a slope map shows it in colour. A slope topographic map adds this layer to the usual topographic map. If you need a free topographic map generator with contour lines, our Contour Map Generator is the topographic map maker for the same square, and the two tools read the same terrain data.

What This Slope Analysis Generator Does

You choose a centre point and a square of 1 to 5 km² around it. The tool loads the terrain tiles that cover the square, turns their colours into heights, smooths them lightly, and works out the slope of every pixel from its eight neighbours. Each pixel then goes into a slope class, and the tool adds up the share and the area of each class. The slope analysis map appears about 12 seconds after your last change, and everything is computed in your browser.

A Free Slope Map, With No Sign-Up

You can use this slope map generator online free of charge, and every file is a free download: there is no account, email or payment. The terrain tiles come straight from a public dataset, the slope map, the downloads and the PDF are made on your device, and a share link holds only the centre, the area and your settings.

Choosing the Place and the Area

Click the map to set the centre, search for a town, an address or a hill, press My location, or load one of the examples. A blue dot marks the centre and a dashed square shows the area. Drag the dot to move the area. The Area slider sets the size from 1 km² (1 × 1 km, the default) to 5 km² (about 2.24 × 2.24 km) in steps of 0.5 km². When you change the place, the area, the classes or the smoothing, the tool waits two seconds for more changes, then loads the terrain and shows a Generating Slope Map wheel for about 10 seconds.

Slope Classes and Units

Slope classes offers 4 classes (under 5%, 5 to 15%, 15 to 30% and over 30%) for a quick planning view, or the 7 classes of the FAO Guidelines for Soil Description for soil, farming and land work. The % and ° buttons show every slope in percent or in degrees, and the m and ft buttons switch the heights, the scale bar and the areas (hectares or acres). These switches change the view at once.

Colours, Relief Shading and the Slope Under the Mouse

Slope colours tints the square by class, from green to dark red, and Relief shading darkens the slopes that face away from a light in the north-west, so the hills stand out. Turn the colours off to see the shading alone. Move the mouse over the square and the badge at the bottom of the map shows the slope at that point, in percent and in degrees, so the map also works as a slope calculator map for any spot in the square. The map styles are Terrain, Street, Satellite and Plain.

Reading the Figures, the Drawing and the Table

The yellow box names the ground by its mean slope (from flat to very steep, using the FAO class names) and gives the shares under 5%, over 15% and over 30%. The cards give the slope at the centre point, the mean and the median slope, the steepest slope (the steepest 0.5% of the area), the share and area under 5%, over 15% and over 30%, and the height range with the relief. The slope drawing shows the square with a north arrow, scale bar and legend, the bar chart shows the share of each class, and the Slope classes table lists every class in percent and degrees with its area and share.

Downloads, Sharing and the PDF Report

GeoTIFF (slope grid) saves the slope of every pixel as 32-bit numbers in the unit chosen at the top, in Web Mercator (EPSG:3857), for QGIS, ArcGIS and other GIS. PNG map saves the coloured, shaded square as a picture, and CSV table saves the class table for a spreadsheet. Copy share link copies a link that opens the same place and settings, and Download PDF report saves a report with the maplity.com letterhead and watermark, the figures, the class chart, the slope map, the table and the method.

The 4 Simple Classes

The default classes split the land at 5%, 15% and 30%. These are the steps that many planning guides, building rules and land assessments use, so the four colours answer the usual first question about a site: is it easy, workable, costly or very hard to use?

These meanings are a general guide. The real limits depend on local rules, soil, rock, drainage and budget, so check with your planning office before you decide on a site.

The 7 FAO Slope Classes

The FAO Guidelines for Soil Description (2006) set the slope classes used in soil surveys around the world. The FAO list starts with four very fine classes below 2% (0 to 0.2, 0.2 to 0.5, 0.5 to 1 and 1 to 2%). Terrain tiles cannot measure such small differences reliably, so this tool joins them into one class, flat, and keeps the other six as they are.

The words in the yellow box (flat, gently sloping, sloping and so on) are these FAO class names, chosen by the mean slope of the whole square.

Percent, Degrees and Ratio

Slope is written in three ways. Percent is rise over run times 100, degrees is the angle of the ground, and a ratio such as 1:12 means one unit up for every 12 across. They are not proportional: 100% is 45°, not 90°, and a vertical wall has an infinite slope in percent. The table converts the common values.

One well-known example: in the United States, the ADA Standards for Accessible Design allow a ramp of at most 1:12 (8.33%), and a walking route steeper than 1:20 (5%) counts as a ramp. You can find such limits on the map with the hover readout and the 5% class edge.

1. Buying land and building a house

Before you buy a plot, a slope map shows how much of it is flat enough for a house, a drive and a garden. Two plots of the same size can be very different: one mostly under 5%, the other mostly over 15% with costly retaining walls.

2. Site planning and grading

Architects and engineers use slope classes to place buildings, roads and car parks on the gentlest ground, and to see early where cut and fill or retaining walls will be needed.

3. Solar farm screening

Ground-mounted solar panels are cheapest on gentle ground, because steep ground needs more grading and stronger mounts. The share of land under 5% or under 10% is a quick first test of a site before a detailed survey.

4. Farming and soil protection

Farmers use slope classes to decide where to plough, where to farm across the slope or build terraces, and where to keep grass or trees to stop erosion. The FAO classes are the standard in soil surveys.

5. Roads, paths and trails

A slope map shows which way a road or a trail can climb gently, where switchbacks are needed, and where a path would be too steep for bikes, prams or wheelchairs.

6. Erosion and landslide risk

Steep ground loses soil faster and is where most landslides start. Slope is the first layer in most erosion and landslide studies, together with soil, rock and rainfall.

7. Forestry and logging

Foresters use slope to choose the harvesting method: wheeled machines on gentle ground, tracked machines on moderate slopes and cable systems on steep ground.

8. Hiking, skiing and outdoor sports

Hikers, mountain bikers and ski tourers read slope to plan routes and avoid steep ground. Slopes of about 30° and more matter for avalanche safety, so the degree view is useful in winter.

9. Urban planning and accessibility

City planners map slope to find streets that are too steep for easy walking or wheelchairs, to place new paths, and to see which parts of a town are hard to reach on foot.

10. Geography teaching

A slope map turns contour lines into colours students can read at once. Compare a flat delta city with a volcano or a canyon, switch between percent and degrees, and see the classes change.

1. Heights From the Terrain Tiles

The tool reads the same AWS Terrain Tiles as our Contour Map Generator, at zoom 15, where one pixel is about 4.8 m at the equator, 3.4 m at 45° and 2.4 m at 60°. Each pixel stores a height in its colour:

Wrong values along tile seams are removed, small gaps are filled, and Light smoothing replaces each height by the average of the 3 × 3 pixels around it. The tool loads two extra pixels around the square, so the pixels on its edge still have all their neighbours.

2. Slope by Horn's Method

For each pixel e, the tool looks at its eight neighbours (a b c in the row above, d and f beside it, g h i in the row below) and uses Horn’s method, the same 3 × 3 formula that GDAL, QGIS and ArcGIS use:

The neighbours next to the pixel count twice as much as the corner ones, which makes the result less sensitive to noise than a simple difference. The Contour Map Generator uses the simpler central differences for its mean slope, so the two tools can differ by a few tenths of a percent.

3. Classes, Shares and the Figures

Each pixel goes into the class its slope falls in (a slope of exactly 5% goes into the 5 to 15% class). The share of a class is its number of pixels divided by the number of pixels in the square, and its area is that number times the ground size of one pixel squared. The mean slope is the average over all pixels, the median is the middle value, and the steepest slope is the 99.5th percentile. The relief shading uses the same window with a light from 315° at 45° above the horizon.

4. Why Pixel Size Changes the Slope

Slope always depends on the distance over which it is measured. Over 3 × 3 pixels of about 4 m, a 2 m high bank is spread over 12 m and looks gentler than it is, and where the source data is 30 m the tiles are already smooth. So the slope map shows the general steepness of the land well, but it misses short steep features and reads lower than a survey on rough ground. Strong smoothing lowers the slopes a little more; Off keeps every detail, including noise.

Elevation Data: AWS Terrain Tiles

The heights come from AWS Terrain Tiles, a free public dataset in the Registry of Open Data on AWS, first built by Mapzen. It merges SRTM (NASA) for most land between 60° N and 56° S, USGS 3DEP in the United States, EU-DEM in Europe, ArcticDEM in the far north, national models from several countries, and global models to fill gaps and the sea floor. The real detail depends on the source for each place, from about 10 m or better in much of the USA to about 30 m in many other places.

Maps and Search

The Terrain and Satellite maps are Esri World Topo Map and Esri World Imagery. The Street map is Maplity’s own vector basemap, built from OpenStreetMap data with Protomaps tiles hosted by KONAKTIVE, with CARTO and OpenStreetMap maps as fallbacks. The Terrain map opens first, at up to zoom 19, and if the Esri maps do not load, the tool switches to the Street map by itself. Place search uses Nominatim, the OpenStreetMap geocoder.

Software Libraries

The map is drawn with Leaflet 1.9, and the PDF is built in your browser by jsPDF. The page runs on Next.js and React. The terrain decoding, the slope and shading maths, the classes, the drawing and the GeoTIFF, PNG and CSV writers are Maplity’s own code.

Limits of the Data

Terrain models measure the ground with a grid, so anything smaller than a few cells, such as a bank, a wall, a ditch or a single building, does not show. Some sources include buildings and trees, which can add steep edges in towns and along forest borders. Over the sea, lakes and wide rivers the tiles hold water depths or the water surface, so a steep sea floor can show near a coast. For construction, boundaries and slope stability, use a land survey or national lidar data.

How These Figures Were Made

The tables show the slope in a 1 km² square (1 × 1 km) around the same 200 famous places that are described on our Contour Map Generator and Elevation Profile Viewer pages. Each row was computed with this tool’s own engine: the default 1 km² square, light smoothing and Horn’s method. Steepest is the 99.5th percentile, and the four shares are the simple classes in whole percent, rounded so that each row adds up to 100. Ground is the FAO class name of the mean slope.

The average mean slope of the 200 squares is 25.4% (24.7% in Europe, 26.0% in the USA). The steepest ground on average is around Grand Teton summit (174.7%), Half Dome summit, Yosemite (143.1%), Matterhorn summit (130.3%), and the flattest around Shark Valley, Everglades National Park (0.3%), Cinderella Castle, Magic Kingdom (0.3%), Statue of Liberty (0.6%). In 91 of the 200 squares at least half of the land is under 5%, and in 91 at least a tenth of the land is steeper than 30%. By mean slope, 15 are flat, 45 are gently sloping, 34 are sloping, 20 are strongly sloping, 26 are moderately steep, 37 are steep, 23 are very steep.

Near coasts and lakes some steep pixels can come from the sea floor or the water edge, because the tiles include depths. In city centres, buildings and bridges in some sources can add short steep edges.

Slope Around 100 Famous Places in Europe

Slope Around 100 Famous Places in the USA

More Free Terrain Tools

• Contour Map Generator: contour lines for the same square, as GeoJSON, KML or DXF.
• Slope and Gradient Calculator: the grade of one path in percent, degrees and a 1:x ratio.
• Elevation Profile Viewer: an elevation chart along a route of up to 5 points.
• Contours to DEM Converter: turn your own contour lines into a DEM grid.
• Map Elevation Finder: click one place and get its elevation.