DC Land Surveyor Exam flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Rule of monuments

In boundary retracement, a located natural or artificial monument called for in the deed generally controls over courses, distances, and area, because the monument is the most reliable evidence of the original location.

Adverse possession elements

Possession must be actual, open and notorious, exclusive, continuous for the statutory period, and hostile to the true owner. Color of title or tax payment may shorten the period in some states.

Accretion vs. avulsion

Accretion is gradual, imperceptible deposit that adds land to the riparian owner. Avulsion is a sudden, perceptible change of channel that does not move the boundary.

Riparian thread of stream

On non-navigable streams, the boundary typically follows the thread (middle) of the channel. On navigable waters, the state generally holds title to the ordinary high water mark.

Ellipsoid height relation

Ellipsoid height h equals orthometric height H plus geoid undulation N, so h = H + N. GNSS gives h; a geoid model supplies N to obtain mean-sea-level heights.

Combined factor

Grid distance equals ground distance times the combined factor, which is the elevation factor (R/(R+h)) multiplied by the projection scale factor at the point.

UTM zone parameters

UTM zones are 6 degrees wide, numbered 1 to 60 eastward from 180 degrees west. The central meridian scale factor is 0.9996 and the false easting is 500,000 meters.

Convergence angle

The angle between grid north and true north. It is zero on the central meridian and grows with distance from it and with latitude; grid azimuth equals geodetic azimuth minus convergence.

Least squares normal equations

The normal equations are N x = A-transpose W L, with N = A-transpose W A. The solution x = N-inverse A-transpose W L minimizes the weighted sum of squared residuals.

A posteriori variance factor

Computed as v-transpose W v divided by (n minus u), where n is the observation count and u the unknown count. A value near 1 indicates weights are consistent with the residuals.

95 percent error ellipse

The standard error ellipse axes come from the covariance matrix eigenvalues. For a 95 percent two-dimensional confidence region, scale both semi-axes by 2.4477.

Compass rule

The compass (Bowditch) rule distributes latitude and departure misclosure proportionally to line length, and is used for ordinary traverses where angles and distances have similar relative accuracy.

Total station reduction

Horizontal distance equals slope distance times sine of the zenith angle. Vertical difference equals slope distance times cosine of the zenith angle.

Prism constant error

A prism constant mismatch, such as 0 mm versus minus 30 mm, biases every measured distance by that fixed amount and must be set to match the prism used.

RTK accuracy and PDOP

RTK typically achieves 10 mm plus 1 ppm horizontally and 20 mm plus 1 ppm vertically. A PDOP above about 6 degrades the solution and should be avoided.

Ground sample distance

GSD equals pixel size times flying height divided by focal length. It defines the ground resolution of a UAV or aerial image and drives mapping accuracy.

Curve formulas

For a circular curve: L = R times delta in radians; T = R tan(delta/2); long chord = 2R sin(delta/2); external = R(sec(delta/2) minus 1).

Area by coordinates

Twice the area equals the sum over all points of (X sub i times Y sub i plus 1) minus (X sub i plus 1 times Y sub i). Coordinates must be listed in order around the parcel.

Meander line

A meander line approximates the water boundary for area computation but is not itself the boundary. The water boundary is the ordinary high water mark or thread of the stream.

Metes and bounds closure

A metes and bounds description starts at a point of beginning, follows bearings and distances around the parcel, and must return to close within an acceptable precision ratio.

Prismoidal formula

Volume equals length divided by 6, multiplied by (A1 plus 4Am plus A2), where Am is the midsection area. It is more accurate than average end area for tapering volumes.

Vertical curve high point

The high or low point of a vertical curve occurs where the grade is zero, at x = minus g1 L divided by (g2 minus g1), measured from the PVC.

Mass diagram balance point

On a mass diagram, the ordinate is cumulative earthwork volume. The balance point where cumulative volume is zero indicates equal total cut and fill.

Catch point computation

The horizontal distance to the catch point equals the grade difference divided by the slope difference, where slopes are expressed as decimals.

Standard of care

The degree of care and skill ordinarily exercised by members of the profession under similar circumstances. It is not a warranty that the survey is perfect.

Seal and signature rule

Only a licensed surveyor may seal work, and only work performed by the licensee or under their direct supervision may be sealed. Sealing other work is an ethics violation.

ALTA/NSPS survey

A land title survey meeting ALTA/NSPS minimum standards, including title commitment review, monumentation, and optional Table A items selected by the client.

Map scale fraction

A representative fraction of 1:24,000 means one unit on the map equals 24,000 units on the ground. Larger-scale maps have smaller denominators and show more detail.

Vector versus raster

Raster data store values in a grid of cells; vector data store points, lines, and polygons. Topology defines adjacency, connectivity, and containment among vector features.

LiDAR bare-earth DEM

LiDAR returns are classified as ground, vegetation, or buildings. A bare-earth DEM is built from ground returns and supports contours and hydrologic analysis.

Chart datum reduction

Soundings are reduced to chart datum, commonly mean lower low water, by subtracting the tide height at the time of the sounding from the observed depth.

IHO S-44 orders

IHO S-44 defines Special Order, Order 1a, Order 1b, and Order 2, each specifying allowable total vertical uncertainty and horizontal uncertainty for hydrographic surveys.

NAVD88 versus NGVD29

NAVD88 is the current U.S. vertical datum, referenced to a fixed benchmark. NGVD29 is the older datum, and the two differ by up to about one meter in places.