Mapping, Platting, and Subdivision Design
Domain 5 covers what a recordable plat must show, how Iowa regulates its approval and recording, and the geometric design checks - curve data, lot area, frontage, drainage - that make a subdivision buildable.
Plat content and approval
- Iowa Code ch. 354 governs plats, including subdivision plats, minor plats, and auditor's plats, and sets the recording framework through the county recorder.
- A recordable plat shows the boundary by bearings and distances with a stated basis of bearing, all lot lines and dimensions, curve data (R, Δ, L, LC, T), monumentation, dedications, the owner's certificate and acknowledgment, and the surveyor's certificate with seal and signature.
- Approval runs through the city council inside incorporated limits (usually after planning commission review) and the county board of supervisors outside them; check setback, frontage, and floodplain requirements before design freeze.
Design checks
Lot area and frontage against zoning; corner radii; cul-de-sac and block lengths; street grades; storm drainage paths; FEMA floodplain and elevation certificates; utility easements; monument preservation.
Worked example
A cul-de-sac frontage lies on a curve with R = 300.00 ft and Δ = 60°, PC at station 10+00.00. T = 300 tan 30° = 173.21 ft L = 300 × 1.0471976 = 314.16 ft LC = 2 × 300 × sin 30° = 300.00 ft PT = 10+00.00 + 314.16 = 13+14.16 Using the 300.00 ft chord as frontage understates the lot's street frontage by 14.16 ft - enough to fail a minimum-frontage test or to misstate an arc-based setback.
Traps
Copying deed bearings that do not close; omitting curve data or the basis of bearing; missing seal or acknowledgment; computing frontage on the chord; failing to recheck lot areas after a design revision; ignoring floodplain notation and benchmark datum on the plat.