What you will make

A map of assessed dollars per acre with a documented denominator and explicit treatment of missing, zero-area, or incompatible records.

A ratio is interpretable only when numerator and denominator refer to compatible records, dates, and units. Assessed value per acre is not market value, development yield, tax rate, or expected return. A 3D extrusion of that statistic is a graphic height, not the building's physical height.

• Calculate parcel area in acres using an appropriate coordinate system.
• Calculate a value-per-acre ratio with clear dollar and area units.
• Explain why a statistical extrusion does not represent physical building height.

Work through the method

1. Check the records

   Inspect parcel identifiers, assessed-value field, valuation date, land-versus-total value definition, and missing-value codes. Confirm that assessment and parcel geometry refer to the same parcels and time period as far as the source allows.

   Check your work: Record the numerator's meaning, source date, and any known exclusions.

2. Calculate parcel area

   Add a decimal field such as Area_Acres and use Calculate Geometry Attributes to calculate polygon area in acres. Select an appropriate local projected coordinate system or a supported geodesic area method and record the choice.

   Check your work: Area values have an explicit unit of acres and plausible nonzero values for valid polygons.

3. Calculate the rate

   Add a decimal field named Value_Acre and calculate assessed value divided by area in acres. Keep the dollar unit explicit, for example assessed dollars per acre. Do not calculate when area is zero or absent; preserve missing values as missing.

   Check your work: A hand-check on one record matches the formula and units.

4. Review outliers and gaps

   Inspect records with null assessed values, zero area, duplicate IDs, unusually high ratios, or values from mixed valuation dates. Do not replace blanks with zero or silently drop records. Note excluded rows and why.

   Check your work: The methods note describes missing and excluded values.

5. Map the statistic

   Use graduated colors for the ratio and label the legend with assessed dollars per acre. Select a classification that does not imply a universal threshold; report the method and class breaks. The mapped rate is descriptive, not a forecast of sale price or development potential.

   Check your work: The legend names the measure and units, and class breaks can be read.

6. Use 3D only as a graphic

   If you have a scene and the layer supports extrusion, you may extrude polygons using the ratio field to emphasize differences. Label the height as a statistical visual encoding, not actual building height, and prefer a 2D map when the height metaphor could mislead.

   Check your work: Any 3D caption explicitly says extrusion height does not represent physical height.

7. Export and state limits

   Export PDF or PNG with source, valuation date, area method, and missing-data note. Include that assessment practices and parcel characteristics vary; this ratio does not establish market value or the feasibility of a project.

   Check your work: A reader can tell what was divided by what and what the ratio does not mean.

Create a parcel-rate map

1. Check the parcel value definition, assessment date, IDs, and missing-value conventions.
2. Calculate area in acres and document the coordinate-system or geodesic method.
3. Calculate assessed dollars per acre only where the denominator and numerator are usable.
4. Map the rate and review missing or extreme records; optionally test an explicitly labeled statistical extrusion.

Bring the method into a product

• PDF or PNG parcel-rate map
• CSV audit table with parcel ID, area acres, assessed value, and ratio

Suggested formats: PDF, PNG, CSV.

Reflect: How could assessment policy or parcel configuration make two similar places look different on this map?

Avoid these mistakes

• Do not divide by zero or treat a missing value as zero.
• A ratio of assessed value to acres is not market value, profitability, or likely development.
• 3D extrusion from the ratio field is not actual structure height.