Valuation & Taxation Base Map

How much of your property tax
reflects what you own,
and how much reflects when you bought?

A map of the official assessment roll. Slide a divider across the same parcels. One side shows assessed value per square foot of land. The other shows the year the land was last reassessed. Both use the same five colours, so where the colour stays the same, the purchase year explains the assessment.

Los Angeles County · 2,372,107 parcels on the 2026 roll Runs on your own servers · no owner names shown

The decision this helps with

Is it worth challenging this assessment?

Before an owner decides to appeal, they need to know which kind of appeal applies. California has two. Each needs different evidence and has a different deadline.

An appeal costs a $46 filing fee and must be lodged within a fixed window. For commercial property, the appraiser's report usually costs far more than both. For most owners the honest answer is don't file, and the app shows why using the county's own figures. For the rest, it shows which question is worth paying an expert to answer.

For: property owners and the advisers who act for them Also useful to: public budget officers

99.3 %of parcels in the county show no fall in value on the current roll. The assessor has already reduced just under 16,000 parcels (0.66 %) to a lower market value.

Most owners would gain nothing from a decline-in-value appeal. A tool that shows this from the county's own data saves them time and fees.

Assessors buy record-keeping systems. Owners can hire appeal firms that take a share of any savings. Few tools let owners check the numbers themselves.

Why neighbours pay such different amounts

A neighbour paying less tax is not, on its own, grounds for appeal.

How Proposition 13 works

Proposition 13 is California's 1978 limit on property tax. A property is assessed at its 1975-76 value, or at its value when it was last bought or newly built. After that, the assessed value can rise by no more than 2 % a year. So two identical houses can carry very different assessments because they were bought in different years.

The courts have upheld it

In Nordlinger v. Hahn (1992), an owner taxed about five times more than her neighbours challenged this rule. The US Supreme Court upheld it, 8 to 1. Large gaps between neighbours are what the law intends.

What the app does with this

It shows how much of a gap comes from the purchase year. A gap caused by purchase year cannot be appealed. A gap the purchase year does not explain may deserve a closer look. The court ruling is quoted on each parcel's card.

The useful question becomes: is my assessment high for a reason I can actually challenge?

The two ways to appeal in California

Two legal routes, with different rules.

Route	The rule	What you need	Deadline
Decline in value "Proposition 8"	The assessed value is the lower of the base-year value (plus the yearly increases) or the market value on 1 January. A reduction is temporary and reviewed each year. (R&TC § 51)	Evidence that today's market value is below today's assessed value. For commercial property this usually means an appraiser's report based on income.	2 July to 30 November
Base-year value	The original base-year value stands unless challenged in the year it was set or the three years after. (R&TC § 80)	Proof that the original base-year value was wrong. A plain factual error, not a matter of opinion on value, can be raised in any year it is found.	Four years, or any time for a factual error

What the appeals board accepts

Under § 402.5, a comparable must be a sale, close in time and place, and no more than 90 days after 1 January. This roll does not publish sale prices.

So the app helps you prepare

Its comparables are similar assessments, not sales. A note above the comparables table explains why they cannot be used as evidence of value. The same note appears in every export.

How the map works

One map, two views, the same colours.

A divider splits the map over the same parcels. On the left, parcels are coloured by assessed value per square foot of land. On the right, by the year the land was last reassessed. Both sides use the same five colour bands, set once for the whole county.

If a parcel keeps its colour as the divider passes over it, its assessment is explained by when it was bought.

band 1under $37 · to 2000

band 2$37–$56 · 2001–04

band 3$56–$72 · 2005–08

band 4$72–$104 · 2009–12

band 5over $104 · 2013–26

The colours stay readable for people with colour blindness, and still work when printed in black and white for an appeal file.

One block (assessor map page 2004-002)4 of its 27 parcels

$ per sq ft of land

$8.6

$154.3

$49.1

$66.5

Year last reassessed

1975

2025

2010

2019

Parcels 1 and 2 keep their colour: explained by the purchase year. Parcels 3 and 4 drop two bands: assessed low for their purchase year. A parcel two or more bands higher on value would read high for its purchase year. The app does not rank or score parcels.

An assessor map page covers roughly one block. Zoomed out, the map shows one point per map page. Zoomed in, it shows each parcel. The colours mean the same thing at every zoom level.

The app

What you see when it opens.

The Valuation and Taxation Base Map when it opens: a notice across the top, the split map over Los Angeles County with the divider at centre, the shared legend below, the list of counties on the left and the summary panel on the right.

Screenshot of the working app, 7 September 2026.

A notice at the top gives the roll year and how many parcels are covered. It also states that the app assembles evidence and a qualified valuer signs any valuation.
All 58 California counties are listed. Los Angeles is covered in full. The other 57 are marked not covered, so they are never mistaken for empty land.
One legend shows the dollar and year range for each colour, so any colour can be checked. Click a band to hide it.
Every count says what it is out of, for example "15,096 of 74,613 map pages in view".
A summary panel updates as you move the map. It shows how much of the variation in view is explained by purchase year.

A worked example

How much is explained by when people bought?

For parcels of the same use on the same block, the app splits the differences in assessed value into two parts: the part that comes from the property, and the part that comes from the purchase year.

typical match between value order and purchase-year order 0.808 (1 = perfect)
parcels where the two differ by two bands or more 33.9 %
counting only parcels on their own lot 26.4 %

In plain terms: on a typical Los Angeles County block, about four fifths of the order in which neighbours are assessed matches the order in which they bought. Two figures are given because in some areas nearly half of homes are units sharing one lot, where a per-lot measure says less.

One block, 2004-00227 near-identical houses

all built 1958–59 · lots 10,983–12,181 sq ft · same use
assessed values $95,955 to $1,764,600, an 18.4-fold spread
per sq ft of land $8.6 to $154.3, a 17.9-fold spread
match with the year each last changed hands 0.92
parcels two or more bands apart 2 of 27, and both read low

On this block, no parcel reads high. The purchase year explains almost all of an 18-fold spread between near-identical houses. The most common result in this app is no case here.

Looking at one property

Pick a parcel to see it beside its neighbours.

Click a parcel and its card shows both bands and a plain-language reading. Its comparables load: every parcel on the same block with the same use and the same lot type. Click a row to jump to that parcel on the map.

The comparables list says what it left out, for example "4 parcels on this page are excluded because their lot status differs". Units sharing a lot are never mixed with parcels on their own lot.
Privacy is protected. The homeowner's exemption is shown only as yes or no, and the street address is never on the same card, so the app cannot be used to link a person to a home.
The § 402.5 note sits above the table, where it will be read.
A shareable link reopens exactly the same view and selected parcel.

The county-wide view

Two things the roll shows on its own.

The county summary page: four headline figures, a chart of parcels by base year from 1975 to 2026 with a tall bar at 1975, a table of the share of parcels still at their 1975 value by place, and the list of 129 records with unusual base years.

Totals on this page are checked against the full roll of 2,372,107 parcels.

163,452 still at their 1975 value

6.89 % of the roll, about one parcel in fifteen, has not been reassessed since Proposition 13 began. The share varies 25-fold across the county, from 16.08 % in one place to 0.63 % in another.

129 records with an odd base year

124 show no valid base year ("0000"), 4 show one earlier than 1975, and 1 shows a year after the roll year. Under § 80, a factual base-year error can be raised in any year it is found.

This is where the roll alone may give an owner something to take to the assessor. The app flags these records as worth asking about. It does not claim the roll is wrong.

Where the data comes from

Why you can trust the numbers.

The official roll

Every figure comes from the Los Angeles County assessment roll as the county publishes it (2026 roll, read on 7 September 2026). Nothing is estimated or modelled.

Source and date on screen

Each number shows where it came from and when. Totals are checked against the county's own parcel counts.

No owner names

The county does not publish owner names, and the app shows none.

One limit to know

The roll has no sale prices, rents or appeal outcomes. Where data is missing, the app leaves the space empty and says why.

Two totals, shown side by side: the app's own net total for the roll is $2.134 trillion. The county announced its 2026 roll at $2.272 trillion across 2,399,978 taxable parcels. Both are quoted as published.

Limits

What this app does not do.

No valuation. It gives no market value, rent or yield. The only money figures are the roll's own. A qualified valuer signs any valuation.
No owner names. Owner identity is never shown.
Not the official record. It does not keep or correct the roll.
One county. Only Los Angeles County is covered. The other 57 are marked not covered.

No sales-ratio statistics. These need sale prices, which this roll does not publish.
No appeal status. No California county publishes appeal filings as data, so the app shows the rules and deadlines only.
Read only. It cannot file an appeal or keep case records.
English only. The colour bands are fixed, so maps stay comparable over time.

Use it for your area

Set it up for
your own county.

We need a parcel data service that carries an assessed value and a base year, and a note of which appeal routes your jurisdiction allows. In about two weeks, the app reads your area instead of Los Angeles.

The parcel source, the two mapped columns, the colour bands and the legal text are all set up without new code. If you already license sales data, it can be added, and comparable sales then become available.

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© 2026 Tabaqat · Built on Strata. Example built on the Los Angeles County assessment roll, read 7 September 2026. Not a market value, a valuation opinion, the official assessment, or advice on whether to file.