2.2 Topographic Surveys, Easements & Encumbrances
Key Takeaways
- Easements convey non-possessory property interests categorized as appurtenant (running with the land to benefit a dominant parcel) or in gross (benefiting an entity such as a utility provider), distinct from dedicated public rights-of-way.
- An ALTA/NSPS Land Title Survey combines boundary, improvement, and title-exception mapping, making it the standard deliverable for commercial acquisition and the document that discloses encroachments.
- An encroachment is physical intrusion of an improvement across a boundary; unlike an easement it conveys no recorded right and may ripen into adverse possession if left unchallenged for the statutory period.
- Topographic surveys must state contour interval, datum, and field-locating method, because LiDAR and UAS photogrammetry return surface models that require ground control and bare-earth filtering before grading design.
- Building, grading, and planting are generally prohibited inside a recorded utility easement, so the easement footprint must be plotted on the base map before any layout is developed.
Topographic Surveys & Modern Survey Technology
A topographic survey maps the 3D relief, physical features, and spot elevations of natural and constructed landforms. Key components include contour lines (lines connecting points of equal elevation), breaklines (linear discontinuities in slope, such as curbs, retaining walls, swale inverts, and ditch ridges), and spot elevations at grade transitions.
Contour Intervals and Precision
The contour interval is the constant vertical distance between adjacent contour lines. Selection of the contour interval is governed by terrain slope, map scale, and project phase:
- 1-foot or 2-foot intervals: Standard for landscape architectural site grading, construction documentation, and architectural layout.
- 5-foot intervals: Standard for large-scale campus master plans, park feasibility studies, or steep mountainous topography.
- 10-foot or 20-foot intervals: Standard for regional watershed planning, GIS environmental suitability models, and USGS 7.5-minute quadrangles.
Surveying Instrumentation
Landscape architects collaborate with land surveyors who utilize specialized electronic and optical instrumentation:
- Total Station: Integrates an electronic theodolite (for measuring horizontal and vertical angles) with an Electronic Distance Meter (EDM). Robotic total stations enable a single surveyor to capture millimetric 3D coordinates using an optical retroreflector prism pole.
- GPS / GNSS (Global Navigation Satellite Systems): Employs multi-constellation satellite receivers (GPS, GLONASS, Galileo). While standalone recreational GPS yields 3- to 5-meter positional errors, Real-Time Kinematic (RTK) GNSS uses an on-site base station or cellular Virtual Reference Station (VRS) network to achieve sub-centimeter to 2-centimeter horizontal and vertical precision.
- LiDAR (Light Detection and Ranging): An active remote sensing technique that fires hundreds of thousands of laser light pulses per second to measure surface elevations. Airborne LiDAR penetrates dense deciduous forest canopies through laser returns that filter out vegetation leaves (canopy model) to generate a high-precision Bare Earth Digital Elevation Model (DEM). Terrestrial Laser Scanning (TLS) captures millimetric 3D point clouds of historic masonry, bridges, and complex rock faces.
- Drone Photogrammetry (UAS): Unmanned Aerial Systems capture overlapping high-resolution aerial photographs. Software uses Structure from Motion (SfM) algorithms to construct 3D point clouds and orthoimagery. Survey-grade drone mapping requires surveyed Ground Control Points (GCPs) visible on the ground to anchor the model to state plane coordinates.
Easements, Rights-of-Way, Encroachments & Encumbrances
Title encumbrances dictate the legally buildable envelope and circulation corridors of any property parcel.
| Encumbrance Type | Definition & Legal Character | Design Impact for Landscape Architects |
|---|---|---|
| Easement Appurtenant | An easement that attaches to and benefits a specific parcel of land (dominant tenement) while burdening an adjoining parcel (servient tenement). Runs with the land automatically upon sale. | Common for shared vehicular access drives, fire lanes, or shared stormwater detention outfalls. Cannot be revoked unilaterally. |
| Easement in Gross | An easement that benefits a specific individual or legal entity (such as a utility company or municipality) rather than an adjoining parcel of land. | Standard for public water mains, sanitary sewer trunks, electric transmission lines, and gas pipelines. Restricts planting of deep-rooted canopy trees or erection of permanent structures. |
| Conservation Easement | A voluntary, legally binding deed restriction conveyed to a land trust or public agency to permanently preserve natural, ecological, scenic, or agricultural resources. | Prohibits future subdivision, commercial development, mass grading, or clearing of native vegetation in perpetuity. Grants tax benefits to the donor. |
| Right-of-Way (ROW) | A strip of land legally dedicated to a municipal, county, or state government for public transportation and utility infrastructure. | Extends beyond the paved street curb to encompass sidewalks, planting verges, street trees, and underground utilities. The property boundary starts at the ROW line, not the curb. |
| Encroachment | An unauthorized physical intrusion of a building, fence, retaining wall, paving, or roof overhang from one parcel onto an adjoining property or easement. | A major legal defect. Unresolved encroachments can ripen into prescriptive easements or claims of adverse possession under state statutory limitation periods (typically 7 to 21 years). |
Public Street Cross-Section & Right-of-Way (ROW) Limits
|<------------------------------ Public Right-of-Way (ROW) ------------------------------>|
| |<--------------- Paved Roadway --------------->| |
| Sidewalk / | Curb Curb | Sidewalk / |
| Tree Verge | Line Line | Tree Verge |
|================|-----------------------------------------------|================|
^ Property Line ^ Property Line
(Client Land) (Adjoining Land)
Real-World Application: When designing streetscapes or commercial plaza frontage, landscape architects must never dimension setbacks from the street curb. The street curb is merely an engineered asphalt or concrete edge that can be relocated during road widening. Setbacks must always be measured from the legal Right-of-Way (ROW) line established on the boundary survey.
Comparison of Survey Methodologies
| Survey Type | Primary Purpose | Standard Deliverable | Typical Horizontal/Vertical Precision |
|---|---|---|---|
| Cadastral / Boundary | Establish legal parcel corners, property lines, and area | Stamped plat with metes and bounds, monument descriptions | 1:10,000 to 1:50,000 relative closure precision |
| ALTA/NSPS Land Title | Satisfy lender and title insurer requirements for commercial acquisition | Multi-layer plat showing boundaries, easements, improvements, Table A data | Meets strict ALTA/NSPS Relative Positional Precision (≤ 2 cm + 50 ppm) |
| Topographic Survey | Map 3D relief, physical features, contours, and spot elevations | CAD drawing with contours (1-2 ft), spot elevations, breaklines, trees | Total Station: ±0.01 ft; RTK GNSS: ±0.03 to 0.06 ft |
| Airborne LiDAR | Large-scale regional surface modeling through dense vegetation | Bare Earth DEM, classified 3D LAS point clouds | ±0.15 to 0.50 ft vertical accuracy (USGS QL1/QL2) |
| Drone Photogrammetry | Rapid site orthomosaic imagery and 3D surface modeling | High-resolution aerial GeoTIFF, DSM, textured 3D mesh | ±0.05 to 0.15 ft horizontally and vertically with surveyed GCPs |
A landscape architect is designing a campus stormwater wetland that discharges by gravity into a municipal concrete culvert. The municipal record drawing from 1974 indicates an invert elevation of 152.80 feet referenced to NGVD29. The current project site survey is referenced to NAVD88. The published National Geodetic Survey (VERTCON) conversion factor for the site coordinates states: NAVD88 = NGVD29 - 1.25 feet. What is the correct invert elevation of the culvert that must be entered into the NAVD88 site grading plan?
An ALTA/NSPS survey for an urban infill site reveals two legal conditions: an adjacent landowner's masonry security wall extends 3.2 feet across the property line onto the subject site without permission, and a regional utility authority holds a recorded 15-foot wide strip across the site for an underground water transmission main. How are these two property conditions legally classified?