2.1 Boundary Surveys, Legal Descriptions & Survey Datums

Land surveying is the legal and mathematical foundation upon which all landscape architectural design, site grading, and physical infrastructure documentation rely. A landscape architect cannot safely place a retaining wall, align a gravity storm sewer, establish a finished floor elevation, or preserve a critical root zone without thoroughly understanding the legal descriptions, geodetic datums, precision limits, and title encumbrances embedded in professional survey documents.

Every boundary line on a site plan represents a legal boundary established by property law, state statutes, and geodetic reference systems. Conflating horizontal or vertical datums, misinterpreting metes and bounds calls, or overlooking recorded utility easements routinely results in catastrophic project outcomes, including structural encroachments, failed stormwater drainage, boundary litigation, and professional liability claims.

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Boundary (Cadastral) Surveys & Legal Descriptions

A boundary survey (also known as a cadastral survey) is an official investigation conducted exclusively by a licensed Professional Land Surveyor (PLS) to establish, retrace, and legally mark the perimeters, property lines, corners, and easements of a real property parcel. Unlike architectural site plans, only a licensed surveyor possesses the legal authority to locate or certify property boundaries.

Metes and Bounds System

The metes and bounds description system is the oldest land surveying method utilized in the United States, prevalent across the original thirteen colonies and states not covered by the public rectangular survey. In this system:

• Metes refers to measured boundary metrics—specifically bearings (directions) and distances (lengths).
• Bounds refers to physical or legal boundary limits, such as natural monuments (rivers, ridgelines, trees), artificial monuments (stone bounds, iron rods), highways, or adjoining property lines.

A metes and bounds description always commences at a legally defined Point of Beginning (POB), which is tied by bearing and distance to a permanent reference monument or street intersection. From the POB, the description traverses the entire perimeter of the parcel sequentially along each boundary call until it returns to the POB ("to the point of beginning, containing 4.35 acres, more or less").

Bearings are recorded in degrees, minutes, and seconds within one of four quadrants (e.g., N 42° 15' 30" E). Distances are historically expressed in engineer's feet and decimal fractions, or legacy survey units:

• 1 Gunters chain = 66 feet = 4 rods = 100 links
• 1 link = 7.92 inches = 0.66 feet
• 80 chains = 1 mile (5,280 feet)
• 1 rod / pole / perch = 16.5 feet

Public Land Survey System (PLSS)

Established by the Land Ordinance of 1785, the Public Land Survey System (PLSS)—frequently called the Rectangular Survey System—covers public domain lands across the Midwest, South, West, and Alaska (30 of the 50 US states). The PLSS subdivides land into standard rectangular grids based on surveyed Principal Meridians (running true north-south) and intersecting Base Lines (running true east-west).

Standard Congressional Township (6 Miles x 6 Miles = 36 Square Miles)
+-----+-----+-----+-----+-----+-----+
|  6  |  5  |  4  |  3  |  2  |  1  |  <-- Section 1 in NE Corner
+-----+-----+-----+-----+-----+-----+
|  7  |  8  |  9  | 10  | 11  | 12  |
+-----+-----+-----+-----+-----+-----+
| 18  | 17  | 16  | 15  | 14  | 13  |  <-- Section 16 designated for public schools
+-----+-----+-----+-----+-----+-----+
| 19  | 20  | 21  | 22  | 23  | 24  |
+-----+-----+-----+-----+-----+-----+
| 30  | 29  | 28  | 27  | 26  | 25  |
+-----+-----+-----+-----+-----+-----+
| 31  | 32  | 33  | 34  | 35  | 36  |  <-- Section 36 in SE Corner
+-----+-----+-----+-----+-----+-----+

Key geometric hierarchy of the PLSS:

1. Townships (Survey): A grid of 6 miles by 6 miles containing 36 square miles (approximately 23,040 acres). Townships are indexed by horizontal Township tiers (North or South of the Base Line, e.g., T3N) and vertical Range columns (East or West of the Principal Meridian, e.g., R4W).
2. Sections: Each township is subdivided into 36 numbered sections, each measuring 1 mile by 1 mile (1 square mile = 640 acres). Sections are numbered using a snake-like (boustrophedonic) sequence starting with Section 1 in the northeast corner, moving west to Section 6, dropping south to Section 7, moving east to Section 12, and ending with Section 36 in the southeast corner. Section 16 was historically reserved for school maintenance.
3. Aliquot Parts: Sections are further subdivided into aliquot fractions:
   • Quarter Section: 160 acres (1/2 mile × 1/2 mile), e.g., the "SE 1/4 of Section 14."
   • Half-Quarter Section: 80 acres, e.g., the "N 1/2 of the SE 1/4 of Section 14."
   • Quarter-Quarter Section: 40 acres (1/4 mile × 1/4 mile), e.g., the "NW 1/4 of the SE 1/4 of Section 14."

ALTA/NSPS Land Title Surveys

An ALTA/NSPS Land Title Survey is a highly detailed, standardized boundary survey jointly established by the American Land Title Association (ALTA) and the National Society of Professional Surveyors (NSPS). Commercial title insurance companies and institutional mortgage lenders mandate an ALTA survey before issuing title policies or capital loans.

In addition to certifying precise boundary lines, an ALTA survey maps all recorded easements, encroachments, rights-of-way, observable evidence of utilities, building footprints, curb cuts, flood zones, and zoning setbacks. The client and landscape architect can specify optional "Table A" items, such as exterior parking stall counts, wetland boundary field locations, building height determinations, and significant specimen tree mapping.

Property Corners, Monuments & the Legal Hierarchy of Calls

When a land surveyor retraces a deed, conflicting legal calls frequently arise between recorded bearings, measured distances, and physical field monuments. Long-standing common law and statutory boundary principles dictate a strict hierarchy of calls to resolve ambiguities:

1. Natural Monuments: Physical geographic features (living marked trees, ocean shorelines, river centerlines, rock outcrops). Natural features hold the highest legal weight because they are immutable natural markers.
2. Artificial Monuments: Human-placed markers (original stone monuments, iron pipes, concrete monuments with brass disks, rebar with surveyor identification caps). Found undisturbed original monuments control over measurements.
3. Calls for Adjoiners: Boundaries of adjacent record properties or dedicated public streets referenced in the deed.
4. Calls for Metes and Bounds (Bearings and Distances): Mathematical courses and distances stated in the written legal description. Between the two, bearings typically yield to distance measurements when reconciling mathematical closures.
5. Area (Acreage or Square Footage): The total stated area (e.g., "containing 12.5 acres, more or less") is considered the weakest legal evidence. Stated acreage yields to all physical monument and measurement calls.

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Vertical & Horizontal Datums & Coordinate Systems

Every elevation and coordinate point on a civil or landscape plan exists relative to a specific mathematical and physical datum. Neglecting datum definitions is a leading cause of engineering and site construction failure.

Horizontal Datums & State Plane Coordinate Systems

A horizontal datum provides the mathematical reference ellipsoid used to calculate geographic coordinates (latitude and longitude) across the Earth's surface.

• NAD27 (North American Datum of 1927): Based on the Clarke 1866 reference ellipsoid, with its origin point fixed at Meades Ranch, Kansas. Legacy civil drawings and USGS quadrangles rely on NAD27.
• NAD83 (North American Datum of 1983): An Earth-centered (geocentric) datum based on the GRS80 (Geodetic Reference System 1980) ellipsoid, compatible with satellite positioning. Horizontal coordinates between NAD27 and NAD83 can shift across the continental US by 10 to 100 meters.
• WGS84 (World Geodetic System 1984): The global standard reference frame utilized by the Global Positioning System (GPS), virtually identical to NAD83 for practical landscape architectural mapping.

To project curved latitude/longitude coordinates onto flat 2D construction drawings without unacceptable scale distortions, the National Geodetic Survey (NGS) established the State Plane Coordinate System (SPCS). SPCS divides the United States into over 120 regional zones, utilizing two primary conformal map projections:

1. Lambert Conformal Conic: Employed for states or zones with predominant east-west geographic extent (e.g., Pennsylvania, Tennessee, Montana).
2. Transverse Mercator: Employed for states or zones with predominant north-south geographic extent (e.g., Illinois, Indiana, Florida).

Vertical Datums: NGVD29 vs. NAVD88

A vertical datum establishes a zero-elevation reference surface (geoid) from which vertical heights and depths are measured.

Exam Trap: Never assume a fixed mathematical difference between NGVD29 and NAVD88. The vertical shift varies regionally across the United States. In Florida, NAVD88 is approximately 1.0 to 1.5 feet lower than NGVD29, while in the Pacific Northwest it is over 3 feet higher. Engineers and landscape architects must use the NGS program VERTCON to calculate the precise mathematical datum shift for their project coordinates. Mixing datums when tying a proposed storm drain into an existing municipal storm sewer will cause slope reversal or drainage ponding!

Benchmarks & Geoid Models

• Permanent Benchmark (PBM): A permanent physical marker (such as an NGS brass disk stamped into a concrete bridge abutment or bedrock) of precisely known vertical elevation above a designated datum.
• Temporary Benchmark (TBM): A stable local reference point established on or adjacent to a construction site (e.g., top of an existing fire hydrant flange, a chiseled square on a concrete curb, or a spike driven into the root flare of an off-site tree) from which all construction elevations are measured.
• Geoid Models: Satellite GNSS/GPS measures ellipsoidal height (h) above the mathematical GRS80 ellipsoid. Modern geoid models (such as GEOID18) calculate the geoid undulation (N) to derive true orthometric elevation (H) (elevation above sea level) via the fundamental relationship: H = h - N.

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