Slope Maps for Building on Sloping Land
How steep is the site, how much of it is actually buildable, and which way does it face? Measured across any New Zealand property from the national 1 m LiDAR elevation model.
Measure a site now
Search an address, click the property, and get slope in degrees plus a distribution across the whole site.
Open the slope tool →“It's a bit sloping” is not a number
Sloping land is priced, designed and consented differently from flat land, and the difference between a 12° site and a 22° site is the difference between a conventional slab and a pole house with a geotechnical report. Yet the information most people have when they make an offer, or brief a designer, is a photograph and an impression.
The elevation data to answer this properly has been public and free since the LINZ National Elevation Programme flew most of the country. What has been missing is a way to point it at one property without installing GIS software.
What slope actually means for a site
Slope is the rate the ground rises or falls, expressed here in degrees. It is worth having a feel for what the bands mean in practice, because the same number carries very different consequences depending on what you are doing.
| Slope | Roughly | What it means on the ground |
|---|---|---|
| 0–5° | 0–9% | Effectively flat. Conventional foundations, easy access, but check drainage — flat ground is where water sits. |
| 5–15° | 9–27% | Gentle slope. Usually workable with cut and fill; driveways still comfortable; good natural drainage. |
| 15–25° | 27–47% | Genuinely sloping. Stepped floors or pole foundations, retaining likely, driveway gradient becomes a design problem. |
| 25–35° | 47–70% | Steep. Geotechnical assessment expected; earthworks costs rise sharply; machinery access is limited. |
| 35°+ | 70%+ | Very steep. Generally retired land, bush or scenery rather than usable area. |
These are orientation, not rules. What governs is your district plan, NZS 3604's limits on what can be built without specific engineering design, and any geotechnical or natural-hazard overlay applying to the site.
Why the distribution beats the average
A single average slope figure is close to useless for a real property. A block that is half flat river terrace and half 30° face averages out to something like 15° — a number that describes no part of the site.
What you want is the distribution: how many square metres or hectares sit in each band. That converts straight into decisions. “62% of this block is under 15°” tells a farmer how much is workable. “There is 900 m² under 8°, in the north-west corner” tells a designer where the house goes. The slope tool returns the breakdown, not just a figure.
Aspect: the half of the answer people forget
Aspect is which compass direction a slope faces, and in New Zealand it matters more than most people expect. Two sites with identical gradient, a few hundred metres apart, can be completely different places to live because one faces north and the other faces south.
- Sun. In the southern hemisphere north-facing slopes collect sun through the day. South-facing slopes stay shaded, and in winter at Southland or Central Otago latitudes a steep south face can see very little direct sun at all.
- Damp and frost. South faces dry slowly, hold frost longer, and grow moss on driveways and decks. It shows up in maintenance and in how a house feels.
- Pasture and planting. Growth rates differ markedly between faces. On a hill-country block, aspect is a large part of why one paddock carries stock and another does not.
- Wind. Aspect combined with the prevailing wind decides exposure — a west-facing Wellington slope and an east-facing one are not comparable propositions.
The slope tool returns a full aspect distribution alongside slope, so you can see what percentage of a property faces each direction rather than guessing from the contours.
The rest of the site assessment
Slope is one layer. These run on the same property boundary, from the same LiDAR.
How to run a slope assessment on a site
- Select the property. Search the address, then click the parcel so the analysis is clipped to the legal title boundary rather than a rectangle that includes the neighbour's bank.
- Check the LiDAR first. Confirm your area has 1 m coverage and note the capture year on the coverage page. Slope from the 8 m fallback is not reliable on gentle ground, and slope from a 2011 survey will not show a 2019 terrace.
- Run slope, then aspect. Look at where the flat ground is, then at which way it faces. The overlap of “gentle” and “north-facing” is usually where you want to be.
- Cross-check drainage. Flat ground at the bottom of a catchment is flat because water put it there. Run the water and drainage tool over the same boundary before you commit to a platform.
- Export for whoever needs it. Contours as DXF for the designer, the terrain report as a PDF for the file, or the raw elevation model if an engineer wants to work with the surface directly.
Where this stops and a professional starts
Slope analysis from LiDAR is a measurement of the ground surface. It is excellent for narrowing options, sanity-checking an agent's description, briefing a designer and understanding what you are looking at. It is not a geotechnical assessment and it cannot see what is under the surface — soil type, groundwater, fill, historic slip material and rock head all matter enormously on sloping land and none of them appear in a DEM.
Where a consent condition, a foundation design or a stability question is involved, this is the input to the conversation, not the conclusion. Engage a geotechnical engineer and a licensed cadastral surveyor.
Related guides
- Contour map of your property — contours clipped to the title boundary, exportable for CAD.
- Terrain checks before buying rural land — the full pre-offer due-diligence pass.
- LiDAR coverage in New Zealand — check resolution and capture year for your area first.
- Elevation lookup — the ground height at a single point.
Frequently asked questions
How do I find out how steep my section is?
Select the property on the map and run the slope tool. It reads the LINZ 1 m LiDAR elevation model across the site and returns slope in degrees for every square metre, plus a distribution showing what proportion of the land falls into each steepness band. That is a more useful answer than a single average, because most sites are a mix of flat and steep rather than uniformly sloped.
What slope counts as a steep site in New Zealand?
There is no single national threshold — it is set by each district plan and by the building method. As rough orientation: under about 5° behaves like flat ground for most purposes; 5–15° is a gentle slope where a conventional platform usually works with modest cut and fill; 15–25° is genuinely sloping and typically pushes you toward pole foundations or stepped floors; over 25° is steep, and geotechnical input becomes unavoidable. Your district plan and NZS 3604 are what actually govern, not these numbers.
Does a council accept LiDAR slope analysis for consent?
For site analysis, context plans, preliminary earthworks assessment and demonstrating which part of a site you are proposing to build on, LiDAR-derived slope is commonly accepted and widely used. For anything where a specific level or a certified platform is a condition — foundation design, finished floor level, retaining wall design, geotechnical assessment of stability — councils require surveyed levels and a suitably qualified professional. Slope analysis tells you what questions to ask; it does not answer the ones that need a stamp.
Why does aspect matter as much as slope?
Aspect is the compass direction a slope faces, and in New Zealand it decides how much sun a site gets. A north-facing slope in the southern hemisphere collects sun all day and dries out; a south-facing slope of identical gradient stays cold, damp and shaded through winter, which affects everything from where you put the living room to whether a driveway ices over. Aspect also drives frost risk, pasture growth, and which side of a hill a house feels liveable on.
Can slope analysis show me where to put the house?
It shows you where the buildable ground is, which is most of the work. Run the slope map, find the areas under your chosen threshold, then check those areas for the things slope cannot see: legal setbacks, overland flow paths, existing services, sun through the day, access grade from the road, and views. The slope map narrows a paddock down to two or three candidate platforms; site knowledge and a designer pick between them.
How accurate is slope calculated from a 1 m DEM?
Slope is a derivative of elevation, so it amplifies whatever error the elevation carries. On steep ground with good LiDAR the result is reliable. On very gentle ground — under about 2° — the model’s own noise becomes a meaningful share of the signal, so treat near-flat readings as approximate. Outside LiDAR coverage, where the 8 m national DEM is the only source, slope on gentle land is not trustworthy at all; check coverage before relying on it.
What does the slope distribution actually give me?
A breakdown of how much of the site sits in each steepness band, as a percentage and as an area. That converts directly into practical numbers: how many hectares of a block are workable, how much of a section is buildable without retaining, or how much of a paddock exceeds the gradient where a tractor is safe.