How HouseScan works it out

The data

The NSW Valuer General publishes about 5.18 million property sales since 2001. We take the Sydney houses from those and match each one to the official NSW Spatial Services cadastre. That gives us about 620,000 houses with their block shape, area, frontage and location.

Then for each block we look up how far it is from a main road and a station, its zoning, the bushfire, flood and landslip layers, and the public school catchment.

How we work out what each drawback is worth

We take houses sold in the same suburb over the same period and compare the ones with a drawback (say, on a main road, a battle-axe block, or a small block) with the ones without it. The difference is then turned into dollars at the price level of this house's suburb. That's why the report gives a range like “makes this one about $X–$Y cheaper”: the same drawback costs more in an expensive suburb and less in a cheaper one.

All drawbacks are compared together, not one at a time, so a small block doesn't soak up the effect of being near a station. Besides how much cheaper or dearer a house is to buy, we also look at growth afterwards. Some drawbacks only make a house cheaper to buy, and it then grows like any other. Others mean it grows less over the long run.

What each drawback is worth is worked out from these sales, compared within the same suburb. The exact coefficients are not published.

How accurate the sales-data estimate is

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The range takes house sales within 1.2 km from the last two years and adjusts each one to this block at today's prices, allowing for price growth over time, block size, frontage, and distance to main roads and stations. It then takes the middle part. If this house has sold before, that sale price is also brought forward to today using the suburb's growth and taken into account.

Track record: locked before the sale, checked after it

A report on a house for sale shows three numbers, kept apart: the sales-data estimate (from the block, the location and nearby sales only, ignoring the asking price), the asking price or price guide (the agent's number, plus any price changes found online), and the most to pay (based on sales evidence; a price guide can't push it up, and once a house has had a price cut the market has already said no to the higher price, so the most to pay won't go back up to it). When the asking price and the sales data are so far apart that we can't tell whether it's the house itself or the price is just off, the report says “not sure” rather than forcing a number.

When HouseScan finds a house for sale and confirms its latest asking price, those three numbers (including any “not sure”) are locked and filed that day and never changed. Once the house sells and the NSW Valuer General publishes the sale price (usually 6–8 weeks after exchange), we compare the two every Monday and post the results here.

Only the first locked call for each house counts, and the contract date has to be after the lock and within nine months of it. The track record gives the error of all three numbers on the same set of houses: the most to pay, taking the asking price as the sale price, and the sales-data estimate alone. Houses marked “not sure” aren't quietly dropped; we show how many there are. Records locked under the old rules before 21 Oct 2026 don't count.

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What we don't know yet

• The house itself. Bedrooms, bathrooms, age, renovations, which way it faces, whether there's a pool: none of this is in public data. New or renovated houses usually sit at the top of the range or above it; ones that need major work sit at the bottom or below.
• Asking prices. For houses for sale, we use public web search results to find the asking price and any price cuts. We don't scrape realestate.com.au or Domain. Search results sometimes disagree with each other, so only the latest asking price counts. Any offer you enter is stored only on your device.
• Official land value history. We haven't added the Valuer General's yearly land values yet, so we can't show how much the land on its own has grown.
• All distances are straight lines. Distances to stations, main roads and your work address are measured in a straight line. Walking or driving will be further.
• Flood maps are incomplete. Only councils that have done a flood study have flood planning maps. “Not mapped” doesn't mean it can't flood.

Data sources and licences

• Sale prices: NSW Valuer General property sales data
• Block boundaries, aerial imagery, contours: NSW Spatial Services
• Zoning, FSR, height limit, heritage, bushfire, flood, landslip: NSW Planning Portal
• Public school catchments: NSW Department of Education
• Stations and roads: NSW transport and road open data
• High-voltage power lines: OpenStreetMap (© OpenStreetMap contributors, ODbL). What's on site is what counts.
• Asking prices, price cuts and public online estimates: public web search results (we don't scrape realestate.com.au or Domain)

Sales data is licensed under CC BY-NC-ND 4.0 and is currently used for a non-commercial preview only. For each dataset's licence and update frequency, see Data sources and licences.

HouseScan is not a formal valuation or advice to buy. Before you make an offer, read the contract, get a building and pest inspection, and if needed talk to a solicitor and a licensed valuer.