S+SNZ Spatial Measurement flashcards

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

Net residential density

The number of dwellings divided by the net residential land area, excluding roads, reserves and non-residential land; expressed as dwellings per hectare.

Sight triangle at intersections

A triangular area at an intersection kept clear of obstructions above about one metre so drivers can see approaching vehicles; its leg lengths depend on approach speeds.

Bulking factor in earthworks

The ratio by which in-situ soil volume increases when excavated and placed as fill, typically 10 to 25 per cent for common soils, used in cut and fill balancing.

Impervious cover and runoff

Increasing impervious surfaces such as roofs and paving reduces infiltration and raises both peak flow and runoff volume, requiring detention or treatment in developed catchments.

Accessible path maximum gradient

Accessible pedestrian routes are limited to a maximum longitudinal gradient of 1:20 (5 per cent); steeper sections must be designed as ramps with landings and handrails.

Sustainable management (RMA)

Section 5 of the Resource Management Act 1991 defines the purpose as enabling people and communities to provide for wellbeing while sustaining resources for foreseeable future needs.

Non-complying activity

An activity that is neither permitted, controlled, restricted discretionary nor discretionary; it needs resource consent and must satisfy the section 104D gateway tests.

Assessment of environmental effects

A report supporting a resource consent application that describes actual and potential effects, including cumulative and temporary effects, and how adverse effects will be avoided, remedied or mitigated.

Designation

A provision in a district plan giving a requiring authority, such as a network utility operator or school board, the right to use land for a specified public work.

Mitigation hierarchy

The ordered sequence of avoiding, remedying then mitigating adverse environmental effects; avoidance is preferred, and offsetting or compensation is considered only after those steps.

Average end area method

A volume calculation that averages the cross-sectional areas at two consecutive chainages and multiplies by the distance between them; suitable where sections change gradually.

Level book arithmetic check

Sum of backsights minus sum of foresights must equal last reduced level minus first reduced level, verifying rise-and-fall or height-of-collimation reductions.

Grade expressed as percentage

Longitudinal grade is the rise or fall divided by the horizontal distance, multiplied by 100; a 2 per cent grade rises 2 metres in 100 metres.

Prismoidal correction

A correction applied to average-end-area volumes for sections that change in shape as well as area, improving accuracy when the two end areas differ markedly.

Combined scale factor

The product of projection scale factor and elevation factor; grid distance equals ground distance multiplied by the combined factor, so ground distance is grid distance divided by it.

Curvature and refraction correction

For spirit levelling the combined correction is approximately 0.067 D squared metres with D in kilometres, subtracted from the staff reading; refraction is about one-seventh of curvature.

PDOP

Position dilution of precision, a dimensionless measure of satellite geometry strength; lower values indicate better geometry and RTK work typically requires values below about six.

RTK GNSS

Real-time kinematic positioning uses carrier-phase corrections from a base station or network to give centimetre-level coordinates in the field, with accuracy degrading as baseline length increases.

Traverse angular misclosure

The difference between the measured sum of traverse angles and the geometrically correct sum; it is compared with the allowable misclosure before the error is distributed.

NZGD2000

New Zealand Geodetic Datum 2000, a semi-dynamic datum aligned to the international terrestrial reference frame; coordinates are accurate at the survey epoch and need deformation modelling over time.

Cadastral survey dataset

The set of survey data, plans, field notes and mark information lodged with Land Information New Zealand to support parcel definition and the creation of new titles.

Easement

A registered right over one parcel of land for the benefit of another, such as a right of way or right to convey services, binding successive owners of both parcels.

Boundary reinstatement

The process of re-establishing an existing cadastral boundary from the official survey record, preferably by recovering original marks before adopting other evidence such as occupation.

Unit title

A form of ownership under the Unit Titles Act 2010 where a principal unit is owned individually and common property is shared, defined by a unit plan deposited with Land Information New Zealand.

Chart datum

The vertical reference for charted depths and drying heights, usually Lowest Astronomical Tide in New Zealand, chosen so water level rarely falls below charted soundings.

Multibeam swath width

Across-track coverage equals twice the depth multiplied by the tangent of half the beam angle, so a 120-degree system covers about 3.5 times the water depth.

IHO S-44

The International Hydrographic Organization standard specifying minimum survey orders, positional and depth accuracies, and coverage requirements for hydrographic surveys intended for navigation.

Speed of sound in seawater

About 1500 metres per second, varying with temperature, salinity and pressure; sound velocity profiles are used to correct echo sounder depths for these variations.

EPSG:2193

The EPSG code for New Zealand Transverse Mercator 2000, the standard projected coordinate system for New Zealand mapping, with a scale factor of 0.9996 on the central meridian.

Vector versus raster data

Vector models store features as points, lines and polygons with attributes, while raster models store values in a grid of cells; raster suits continuous surfaces and vector suits discrete features.

Spatial join

An operation that appends attributes from one dataset to another based on their spatial relationship, such as point-in-polygon, rather than on a shared attribute key.

DEM, DSM and DTM

A digital elevation model represents surface heights; a digital surface model includes vegetation and buildings; a digital terrain model is a bare-earth representation with above-ground features removed.