How to Read a Plat and a Survey

Why this matters

The fence is not the property line, the edge of the mowed grass is not the property line, and the customer's confident wave toward the neighbor's shed is not the property line. Equipment pads, trenches, sheds and generators get placed against setbacks and easements that exist only on paper, and the paper is a plat or a survey the customer usually already owns. A tech who can read one in five minutes places equipment where it can stay, and knows the exact point at which tape-measuring stops being good enough and a licensed surveyor has to come out.

Two documents that look alike

A plat (or subdivision plat) is the recorded map that created the lots. It shows each lot's lines as designed, the street right-of-way, easements dedicated to utilities and drainage, platted building setback lines, and general notes. It is filed with the county and binds every lot in the subdivision.

A survey is a licensed surveyor's drawing of one parcel at one date: the lines as located in the field, the monuments found or set, and usually the improvements (house, driveway, fence) with their distances from the lines. A boundary survey is the full product. A mortgage location survey or similar lender product is a lighter one, and it often carries a note that it is not to be used to establish fences or improvements. Read that note; it tells you how much the drawing is worth for your purpose.

The plat tells you what the lot is supposed to be. The survey tells you what was on the ground, and where, the day someone measured it.

The procedure

1. Get the document and read the title block first. Find who prepared it, the date, the surveyor's seal or the recording information, and the parcel it describes. Reason: a survey from before an addition or a lot-line adjustment shows a house and lines that no longer exist. A drawing with no seal and no recording stamp is a sketch, not a record. Skip this and you will place equipment against a line that moved.

2. Orient it. Find the north arrow, the scale, and the street name. Turn the drawing so north matches the ground. Reason: everything else is read in that frame, and the rear yard on a lot that faces south is the north side of the house, which decides shade, wind and snow at the equipment. See related: Microclimates on One Lot.

3. Read each lot line as a bearing and a distance. A line is labeled with a bearing, its direction as an angle east or west of north or south, and a distance in feet to the hundredth. "N 89 deg 58' 10" E 80.00'" means a line running a hair north of due east for 80 feet. Some surveys show two distances: (R) for the record figure from the deed or plat and (M) for the figure the surveyor measured. Reason: the bearings tell you the lot is not a perfect rectangle and the house may not sit square to it, so a distance taken square off the house wall is not a distance from the line. A difference between record and measured of a few hundredths of a foot is routine; tenths are worth noting; a foot or more is a question for the surveyor.

4. Find the monuments. Corners are marked with monuments, usually an iron pin or pipe, abbreviated IPF (iron pin found), IPS (iron pin set), or a concrete monument (CM). They are typically a few inches below grade, and a metal detector or a probe finds them. Reason: a monument is the only field reference that ties the drawing to the ground. A pin bent by a mower, pulled by a fence crew or buried under a driveway can sit a foot or more from where it was set, so one pin alone proves little; two pins and a cross-check against a mapped improvement prove a lot.

5. Read the easements and setback lines. Easements are drawn as dashed lines parallel to a lot line, labeled with their width and purpose: "10' U.E." for utility, "D.E." for drainage. A platted building setback line (B.S.L.) is drawn the same way along the front. Reason: an easement limits what may be built in the strip; a platted setback line limits where the house may go. The zoning ordinance sets its own setbacks too, and where the plat and the zoning code differ, the stricter one governs. Each has its own card: See related: Utility Easements and What the Utility Can Make You Move.

6. Read the notes block. Plats and surveys carry notes: the flood zone and map panel the surveyor checked, restrictions on fences or structures, the source of the bearings, encroachments found. Reason: the note is often the only place an easement's terms are written, and a flood-zone note is a date-stamped statement you will want to re-check against the current map rather than trust.

7. Read any curve as a curve table entry. Lots on cul-de-sacs and curving streets have lines that are arcs, labeled C1, C2 and so on, with a table giving radius, arc length, central angle and chord. Reason: a straight tape between two pins on a curved front line measures the chord, which is shorter than the arc. For placing equipment near a curved line, the chord is the conservative side only when the arc bows outward from the lot; when it bows inward, your tape line cuts into the setback.

8. Measure from the monuments, and decide whether that is good enough. Pull a string between two found pins on the controlling line and measure square off the string to the proposed position. Cross-check by measuring to an improvement the survey dimensions, such as a house corner. As a shop default, call a licensed surveyor to stake the line when the planned position will sit within 2 feet of a line that controls it, when fewer than two pins can be found, or when your cross-check disagrees with the survey by more than about half a foot. Reason: a tape from pins is an estimate; only a licensed land surveyor can locate a boundary, and a position that depends on the estimate being right to the inch should not depend on a tape.

9. Write it on the job. Record the document used (type, date, preparer), the pins found, the cross-check result, and the distance from each controlling line. Reason: if a neighbor or an inspector questions the placement, the shop can show what it relied on.

A simplified survey

 IPF          REAR LINE  N 89d58'10" E  80.00'        IPF
  o--------------------------------------------------o
  |  - - - - - - - - 10' UTILITY EASEMENT - - - - -  |
  |                                                  |
  |                   rear yard                      |
  |           +---------------------------+          |
  |  22.4'    |                           |  22.6'   |
  |<--------->|          HOUSE            |<-------->|
  |           |                           |          |
  |           +---------------------------+          |
  |  . . . . . . 25' BUILDING SETBACK LINE . . . . . |
  |                                                  |
  o--------------------------------------------------o
 IPF         FRONT LINE (STREET R/W)  80.00'         IPS
 WEST LINE and EAST LINE: N 00d02'15" W  120.00'

The side distances leave a house 35.0 feet wide (80.00 minus 22.4 minus 22.6), and a distance like the 22.6 to the east wall is the mapped improvement that step 8 cross-checks against.

A worked example: placing a pool equipment pad

The customer wants a 4 by 6 foot pool equipment pad in the rear yard near the east side, out of view of the patio. The office pulled the boundary survey from the customer's closing papers: prepared by a licensed surveyor eleven years ago, sealed, matching the drawing above. The house has had no additions since, per the permit history.

Orientation. The side lines run N 00 deg 02' 15" W, essentially due north, so the rear yard is the north side of the house. The pad will sit in the house's shade most of the day, which matters for the pool heater's air intake and not at all for the pump.

The constraints. The plat shows a 10-foot utility easement along the rear line. The zoning ordinance, read on the town's site, requires pool equipment to sit at least 5 feet from side and rear lines. Along the rear, the easement is the stricter of the two at 10 feet; along the east side, the 5-foot setback governs.

Pins. The tech finds the iron pin at the northeast corner with a metal detector, 3 inches down, and the pin at the northwest corner. A tape between them reads 79.86 feet against the record 80.00, a difference of 0.14 feet, under 2 inches. The tech also finds the southeast pin and pulls a string along the east line.

Cross-check. The survey puts the house's east wall 22.6 feet from the east line. The tape from the wall to the string reads 22.5 feet, 0.1 foot short (22.6 minus 22.5). That is inside the half-foot cross-check tolerance, so the pins have probably not been disturbed.

First placement. The customer's preferred spot puts the pad's back edge 11.5 feet from the rear line and its side edge 6 feet from the east line. Margins: 11.5 minus 10 leaves 1.5 feet from the easement; 6 minus 5 leaves 1 foot from the side setback. Both are under the shop's 2-foot default, so this placement would need a surveyor to stake the lines before the pad is formed.

Second placement. The customer agrees to move the pad 1 foot south and 1.5 feet west: back edge 12.5 feet off the rear line, side edge 7.5 feet off the east line. Margins: 12.5 minus 10 leaves 2.5 feet; 7.5 minus 5 leaves 2.5 feet. Both clear the default, the pins agree with the record, and the cross-check holds, so a tape from the pins is good enough for this pad. The job notes record the survey's date and preparer, the three pins found, the 0.14-foot record difference, the 0.1-foot cross-check, and both final distances.

What would have sent this to a surveyor anyway. Finding only one pin. A cross-check that read 21.8 feet instead of 22.5, which would mean the string, the pins or the survey is wrong by most of a foot. A customer who insisted on the first placement. Or a fence that sits well off the surveyed line, which is a sign the neighbors may disagree about where the line is, and a pad placed against a disputed line is placed in the middle of somebody else's argument.

What the drawing will not tell you

A plat or survey does not show buried utilities; that is a one-call locate. It may not show easements recorded after its date, or a prescriptive easement that was never written down. And it does not show what the zoning ordinance requires for your specific equipment, which has to be read separately. The drawing is the frame; the other records fill it in. See related: The Public Record of a House and How to Read It.

References

• The recorded subdivision plat and the parcel's boundary survey, from the county recorder or the customer's closing documents
• The state board that licenses land surveyors, for who may locate a boundary
• The local zoning ordinance, for equipment and accessory-structure setbacks
• See related: Utility Easements and What the Utility Can Make You Move; Property Lines, Easements and Where Equipment Can Go
• See related: Locate the Utilities and Shutoffs First