Illinois exam concept: national valuation

Plottage vs. assemblage

Assemblage is joining parcels. Plottage is the added value the combination creates. Keep the process, the whole site's value and the extra value separate when you answer an exam question.

Last reviewed: October 24, 2026

What is the difference?

Assemblage names the process. Plottage value names the gain. If an owner joins two neighboring lots, the owner has assembled land. If that larger site is worth more than the lots were worth separately because it offers better utility, the excess is the plottage increment.

Read the task before choosing the term
Question asks for	Answer	What it identifies
The act of joining parcels	Assemblage	The process, even if no value gain follows
The added value created by joining	Plottage value or increment	Only the excess over separate values
The value of the whole assembled site	Combined market value	The starting total plus any increment
Whether the buyer made money	Financial result	Prices paid, costs and proceeds, not just the increment

Example: Two narrow commercial lots might become more useful together because the wider site can fit a building and legal access. Buying the second lot is part of assemblage. The extra market value from the more useful site is plottage value. The numbers still have to support that gain.

Some appraisal references use the terms together or use assemblage value for the value effect. When a question contrasts the process with its added value, use the distinction above. Do not choose solely because one word appears in the story.

How do you calculate the plottage increment?

Plottage increment = assembled market value − total separate market values

Add every separate value first. Subtract that total from the assembled value. The answer is the increase, not the entire value of the assembled land.

Assume both separate values and the assembled value refer to the same valuation date and consistent property rights and conditions. Use the problem's figures rather than inventing a future zoning approval or mixing today's values with a later completed-project value. These are invented exam figures, not current Illinois land prices.

Worked example: two lots become a more useful site
Step	Calculation	Result
1. Total the separate values	$180,000 + $220,000	$400,000
2. Read the assembled value	Value given in the problem	$500,000
3. Find the increment	$500,000 − $400,000	$100,000
4. Find the percentage increase, if asked	($100,000 ÷ $400,000) × 100	25%

Do not solve a different question. If asked for assembled value instead of the increment, add the separate total and the increment: $400,000 + $100,000 = $500,000.

The percentage base is the separate-value total. Dividing $100,000 by $500,000 gives 20%, which is the increment's share of the final value. It is not the 25% increase over the starting value.

If the combined value were $400,000, the difference would be zero. If it were $380,000, the difference would be negative $20,000. Neither establishes a positive plottage gain. Use the result supplied by the figures, even when it is zero or negative.

Why plottage value is different from profit

Keep the same market values: $400,000 separately and $500,000 assembled. Now suppose the buyer pays $450,000 to acquire the lots and incurs $30,000 of additional assembly costs, such as closing and holding costs. Assume these costs are separate, counted once and do not buy new improvements that would change the stated $500,000 value. The plottage increment remains $100,000. The separate spending comparison is $500,000 − $450,000 − $30,000 = $20,000.

That $20,000 is a simplified value-minus-stated-cost balance, not a promise of realized net profit. Financing, holding time, selling expenses, taxes and other items may change the result. Do not subtract the $400,000 separate-value total again after deducting the $450,000 purchase price; those are different measures of the same land.

In an actual analysis, check whether an estimated value already reflects a condition or cost. Subtracting that allowance a second time distorts the result. A buyer who pays a premium for a needed parcel has spent more, but that payment alone does not prove an equal increase in market value.

What could make the combined site worth more?

Identify a usable advantage, then test whether buyers would pay for it. Better shape, frontage or access may help. A hoped-for building that cannot be permitted, financed or supported by demand does not establish the same value as an approved, feasible project.

Legal: Does the intended use fit the applicable zoning and other restrictions?
Physical: Does the site actually accommodate the use, including access and practical site conditions?
Financial: Can the use justify its costs?
Productive: Does it support the highest value among the uses that pass the other tests?

These highest-and-best-use checks are supported by the Fannie Mae site-appraisal guidance. That guide addresses mortgage appraisal; it does not grant development permission or guarantee an Illinois site's value.

A price rise without a parcel combination does not establish plottage. If each lot rises in value because the whole local market improves, that is a different explanation for the increase. The question must connect the extra value to the assembled site.

Keep tax records separate from the value question. Cook County has a division and consolidation process for tax parcels. Its FAQ notes that one residence can have multiple PINs and that filing a consolidation does not change or reduce the overall assessment or taxes due. A PIN change is not a measurement of plottage or evidence that a particular development has been approved.

Five original practice questions

Choose an answer before opening the explanation. Then answer the changed-fact version. These questions are original study examples, not actual or recalled PSI questions.

Question 1 of 5 · Action or result

An investor buys three adjoining lots and brings them under one ownership. The question asks for the name of that process. Which answer fits?

Plottage increment
Assemblage
Subdivision
Depreciation

Show answer and explanations

Answer: B. Assemblage

Why this misses: This names an added-value amount. The facts ask what the investor is doing, without establishing any value gain.
Correct. The investor is joining parcels. Whether that combination creates extra value is a separate question.
Why this misses: Subdivision divides land. This investor is bringing existing parcels together.
Why this misses: A loss in value does not name the parcel-combination process.

Change the facts: If the question instead asks for the supported increase in value caused by the combination, choose plottage value or plottage increment.

Definition reference: IAAO glossary. Calculations and scenarios are original examples.

Question 2 of 5 · Dollar increase

Two lots have separate market values of $180,000 and $220,000. At the same valuation date and on a consistent basis, the assembled site is worth $500,000. What is the plottage increment?

$500,000
$400,000
$900,000
$100,000

Show answer and explanations

Answer: D. $100,000

Why this misses: That is the value of the whole assembled site, not the extra value from combination.
Why this misses: That is the sum of the separate values. It is the comparison base, not the increment.
Why this misses: Adding separate and assembled values counts the same land twice.
Correct. $500,000 minus ($180,000 plus $220,000) leaves $100,000 of added value.

Change the facts: If the assembled value is $400,000, the difference is zero. The combination has not created a positive plottage increment.

Definition reference: IAAO glossary. Calculations and scenarios are original examples.

Question 3 of 5 · Percentage base

The separate values total $400,000 and the assembled value is $500,000. What is the percentage increase over the separate-value total?

25%
20%
125%
5%

Show answer and explanations

Answer: A. 25%

Correct. Divide the $100,000 increment by the $400,000 original total, then multiply by 100.
Why this misses: That divides the increment by the assembled value. It answers what share of the final value is extra, not the requested increase over the starting total.
Why this misses: That describes the final value as a percentage of the starting value. The increase alone is 25%.
Why this misses: Dividing the final value by the increment does not calculate the requested percentage increase.

Change the facts: If the question expressly asks what percentage of the final $500,000 value is the increment, the denominator changes to $500,000 and the answer becomes 20%.

Definition reference: IAAO glossary. Calculations and scenarios are original examples.

Question 4 of 5 · No automatic premium

A buyer joins two lots worth $150,000 each. The assembled site is worth $300,000 because its permitted use and utility are unchanged. What has been established?

A $300,000 plottage increment
A mandatory premium for common ownership
Assemblage with no positive plottage increment
A subdivision into smaller lots

Show answer and explanations

Answer: C. Assemblage with no positive plottage increment

Why this misses: This confuses the whole site's value with the increase over the separate values.
Why this misses: The facts supply no premium. One owner does not by itself create extra market value.
Correct. The parcels were joined, but $300,000 minus ($150,000 plus $150,000) is zero.
Why this misses: The buyer is combining parcels, not dividing them.

Change the facts: If the combined value is only $280,000, the difference is negative $20,000. Report a loss relative to the separate total, not a positive plottage gain.

Definition reference: IAAO glossary. Calculations and scenarios are original examples.

Question 5 of 5 · Value versus spending

Separate market values total $400,000 and assembled market value is $500,000. The buyer actually pays $450,000 and incurs $30,000 of additional costs, with no cost counted twice. Which statement distinguishes the value increment from the simplified value-minus-cost balance?

Both amounts are $100,000.
The increment is $100,000; the simplified balance is $20,000.
The increment is $20,000; the simplified balance is $100,000.
Both amounts are $50,000.

Show answer and explanations

Answer: B. The increment is $100,000; the simplified balance is $20,000.

Why this misses: The value increment is $100,000, but the buyer's stated spending totals $480,000.
Correct. Compare market values for the increment: $500,000 minus $400,000. Compare value with stated spending for the balance: $500,000 minus $450,000 minus $30,000.
Why this misses: This reverses the market-value comparison and the spending comparison.
Why this misses: $50,000 ignores the separate-value total in the increment and ignores $30,000 of costs in the spending comparison.

Change the facts: If the buyer pays $490,000 and the same additional costs are $30,000, the simplified balance is negative $20,000. The stated market-value increment remains $100,000.

Definition reference: IAAO glossary. Calculations and scenarios are original examples.

Plottage and assemblage FAQ

What is the difference between plottage and assemblage?

Assemblage is joining parcels. Plottage value is the extra value from the combination, above their separate-value total. A successful purchase can complete the process without creating that extra value.

What is the formula for plottage increment?

Subtract the sum of the parcels' separate market values from the market value of the assembled site. Compare values on a consistent date and basis. Do not substitute purchase prices unless the question identifies them as the separate values to use.

Does assemblage always increase value?

No. The assembled value may be greater, equal or lower. More land does not automatically mean a useful additional building area, legal access, permitted density or sufficient demand.

Is plottage the same as profit?

No. A value increment compares market values. The buyer's financial result depends on acquisition prices, other costs, timing and eventual proceeds. A positive increment can coexist with an unprofitable purchase. If those costs were already allowed for in a stated value or cost total, do not deduct them again.

Must the parcels be adjoining?

Typical plottage examples use adjoining parcels made useful as one larger site. IAAO's broader assemblage definition also allows parcels that are not contiguous. Merely owning unrelated properties does not prove a plottage increment.

Does combining tax PINs prove plottage?

No. A tax-parcel change does not calculate the market-value gain. Cook County treats tax divisions and consolidations as a separate application process. Its FAQ says filing a consolidation will not change or reduce the overall assessment or taxes due. This is Cook County guidance, not a statewide procedure.

How many plottage questions are on the Illinois exam?

PSI does not publish a separate count for plottage. This concept fits national III.B.1, economic principles and property characteristics affecting value. The entire Valuation area is 8% of the 100 scored national questions, not eight questions about plottage. The five questions here are original practice.

Choose the next concept from the mistake

If you mixed up the process and the value effect, explain the distinction without the example figures. If the arithmetic was wrong, write the separate-value total on its own line before subtracting. For other value effects, see progression and regression. For choosing a valuation method, use the three appraisal approaches.

If phone practice would help you revisit these concepts, you can download Pass Illinois. The full lesson and answers remain available here.

Sources and scope

Reviewed October 24, 2026. The definitions are general appraisal concepts, not a new October 2026 Illinois rule. PSI places economic principles affecting value in national III.B.1. The whole Valuation area is 8% of the 100 scored national questions. There is no published plottage-only question quota.

The IAAO glossary is dated 2022; the Fannie Mae section is dated June 4, 2025. The DRE chapter is an older general reference and is not used here for current appraisal standards or California law. Cook County guidance describes that county's tax process. None of these examples is an appraisal, investment recommendation, survey, title opinion or development approval.

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