vaadagai.homes

How rent data is calculated

Every number on vaadagai.homes comes from renters reporting what they pay - it is not independently verified. This page explains exactly how a report becomes a published median, so you can judge any figure for yourself.

What qualifies as a report

A report is one renter marking their flat on the map and entering the monthly rent, the size (1RK, 1, 2, 3, or 4+ BHK), and a few optional details like deposit, parking, and water source. No account, no sign-in, and no personal identity is attached. The location is rounded to about 110m before it is stored, so the point shows the block, never the door.

A rent has to be at least plausible to be stored at all: anything below ₹2,000 or above ₹5,00,000 a month is rejected outright as a typo or a joke. Values inside those limits but outside the normal range for their size are kept but held aside - see “unusual reports” below.

Minimum sample size for a median

An area needs at least 5 reports of the same size before any median is shown for that size. Below that floor, the individual pins are still on the map, but no summary number is published - a “median” off one or two rents is noise wearing a number’s clothes. The same floor applies to the deposit, parking, and water-source summaries.

How the median is computed

The headline figure is a corroboration-weighted median: a rent counts for more as independent nearby reports (within ±12%) agree with it. A tight, agreed-upon cluster carries the number; an isolated high or low barely moves it, which blunts both honest mistakes and planted pins. Alongside it we show the raw 25th–75th percentile spread - the range the middle half of renters pay - so a genuinely wide or two-sided market stays visible instead of hiding inside a single number.

What low / medium / high confidence means

A median off 5 reports deserves less trust than one off 40, so each is labelled by how many reports it rests on:

  • Low - 5–9 reports. A rough signal; treat it as a starting point, not a settled number.
  • Medium - 10–24 reports. A reasonable read on the area for that size.
  • High - 25 or more reports. Well sampled; the median is stable.

How stale reports are labelled

Rents age. A rent agreed a year or more ago says little about what a landlord asks today, so any report older than one year is marked “over a year old”. Stale reports are not deleted - they are real rents someone paid - but where a median leans on them, the page shows how many of the reports behind it are that old, so you can weigh the number accordingly.

How unusual reports are handled

A report that lands outside the normal range for its size, or more than 2.5× above or below the local median, is accepted onto the map but flagged and held out of the median until reviewed, shown in amber as “unusual”. Keeping it visible but excluded is deliberate: hiding it would erase a genuine outlier, while counting it would let a few extreme entries drag the number.

From there, a report is removed if 2 or more people report it as wrong, or if it stays extreme once the surrounding area has enough clean data to judge it against. A flag that no one resolves and that new data never vindicates is set aside after 30 days as “unconfirmed” - still shown in amber for transparency, still kept out of every median - rather than sitting in a queue forever.

The groundwater-quality layer

The map has an optional groundwater quality layer (the 💧 toggle). Unlike everything else on this page, it is not renter-reported: it comes from the Central Ground Water Board (CGWB), the government body that samples monitoring wells across India, published via the National Water Data Portal (India-WRIS). We bake a snapshot into the site and refresh it occasionally by hand - the app never calls their service while you browse. It currently rests on 93 wells inside the Chennai metro, read between 2000 and 2022. Every area is ranked on the Chennai water quality page.

The colour is TDS(total dissolved solids) - roughly how much salt and mineral is in the water, the thing that makes borewell water hard or brackish. Bands follow BIS IS 10500, India's drinking-water standard (500 mg/L acceptable, 2000 mg/L the outer permissible limit):

  • Fresh (under 500 mg/L) - Within the drinking-water limit. Soft to moderately soft.
  • Slightly hard (500-1,000 mg/L) - Above the ideal limit but usually fine with basic filtering. Some scaling.
  • Hard / brackish (1,000-2,000 mg/L) - Hard water. An RO unit is the norm here; taste and scaling are noticeable.
  • Very saline (over 2,000 mg/L) - Beyond the permissible ceiling. Not for drinking without treatment; borewell water often tastes salty.

Most wells record electrical conductivity but not TDS directly, so where TDS is missing we estimate it as 0.64 × conductivity - the standard factor for natural groundwater. These are flagged as estimates in the underlying data.

What the fade means (confidence). 93 wells is sparse, so the colour between them is interpolated - a weighted average of nearby wells, not a measurement. The more faded a patch, the further its nearest real well, and the less you should trust it:

  • High - a real test well within 1.5 km.
  • Medium - nearest well 1.5-4 km away.
  • Low - nearest well 4-6 km away.

Past about 6km from any well we paint nothing rather than guess, so blank areas mean "no nearby data", not "good water". The hollow dots mark the real wells.

Two cautions worth repeating: this is groundwater, not your piped Metrowater tap supply, and groundwater TDS swings with the seasons and the monsoon - a dry-summer reading can be far saltier than the same well after the rains. Treat the layer as orientation, not a lab test of a specific building.

Source: Central Ground Water Board (CGWB), Ministry of Jal Shakti, Government of India, via the National Water Data Portal. Used under Government open-data terms.

The flood-risk layer

The map has an optional flood risk layer (the 🌊 toggle). Like groundwater, it is not renter-reported: it is a modelled flood-hazard map from the Greater Chennai Corporation, published on the OpenCity urban-data portal. We bake a simplified copy into the site; the app never calls their service while you browse.

What "10-year" means. This is a modelled 1-in-10-year rainfall scenario — a storm with roughly a 10% chance of being equalled or exceeded in any given year. It is not a record of 10years of observed floods. The model grades each patch into three hazard classes — High, Moderate and Low:

  • Low — The lowest of the model's three hazard levels.
  • Moderate — The middle of the model's three hazard levels.
  • High — The highest hazard level the model assigns.

The source grades the zones High / Moderate / Low but does not publish the depth or duration thresholds behind those labels, so we show them only as relative levels and never attach an inundation depth to them.

The published layer has 99 high, 175 moderate and 403 low zones. The zones nest (a high-risk core inside a wider low-risk patch), so the map paints the worst category on top at every point. On a locality page we report the shareof the area within 1.5 km of the centre that falls in any zone, rather than a single label, because low-level zones are widespread and one "high" stamp would flatten real differences between areas.

The data is a Greater Chennai Corporation model and does not state its exact extent. Where no zone appears, that means "not modelled here"— the area may be outside what the model covers, or a small flood-prone patch may fall between our sample points — not"no flood risk". Treat the layer as orientation at the neighbourhood level, not a verdict on a specific building, and never as a guarantee either way.

Source: Greater Chennai Corporation flood-hazard zones (10-year return period), via the OpenCity urban-data portal (data.opencity.in). Public-domain open data.

Limitations

  • The data is renter-reported and not independently verified. Treat every figure as an estimate.
  • Locations are rounded to about 110m, so a pin marks a block, not a specific building.
  • Thinly sampled areas can move as more reports arrive; the confidence label tells you which those are.
  • Rents on the marketplace are owner asking prices and are separate from this renter-reported map.
  • The groundwater layer is interpolated from a handful of government wells and is not tap water - see the groundwater section above.
  • The flood-risk layer is a modelled 1-in-10-year scenario over the GCC area, not observed floods; a blank area means "not modelled", not "safe" - see the flood-risk section above.
  • Always confirm the current rent directly before you sign anything.

Think a number is wrong, or want a report removed? Here is how to report it. More on the project is on the About page.