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Surveying Terms

This page defines surveying domain terminology that appears in the Benchmrk application and documentation. Each term includes context for how it relates to data you will encounter in the platform.

Benchmark​

A survey mark established at a known elevation (height above a reference datum) used as a vertical reference point. Benchmarks are typically brass or metal discs set into stable structures like bridge abutments, building foundations, or concrete pillars. In Benchmrk, benchmarks appear as a distinct mark type in the Layer Manager symbology. The point details panel shows their elevation data, vertical class, and the datum they reference.

Cadastral Survey​

A survey that defines and records the boundaries of land parcels for legal and administrative purposes. Cadastral surveys establish property boundaries, easements, and rights of way. While Benchmrk does not display cadastral boundaries directly, many survey marks in the platform were originally established as part of cadastral surveys. The mark metadata may reference the cadastral survey plan that established or used the mark.

Coordinate Reference System​

A framework that defines how coordinates (numbers) map to actual locations on the Earth's surface. A CRS includes a datum (the mathematical model of the Earth), a projection (how the curved surface is flattened to a 2D map), and a coordinate system (the axes and units used). In Benchmrk, survey marks store coordinates in specific CRS formats. The platform primarily uses GDA2020 with MGA zone projections, and the point details panel displays coordinates in both projected (Easting/Northing) and geographic (Latitude/Longitude) formats.

Easting/Northing​

Projected coordinates expressed in metres within a Map Grid of Australia (MGA) zone. Easting is the distance east from the zone's central meridian (with a false easting of 500,000 m to avoid negative values). Northing is the distance north from the equator (with a false northing of 10,000,000 m in the southern hemisphere). In Benchmrk, the point details panel displays Easting and Northing values for survey marks alongside their MGA zone number, giving you precise metric coordinates suitable for fieldwork and engineering calculations.

Geodetic Datum (GDA2020/GDA94)​

A mathematical model of the Earth's shape and size used as the reference framework for coordinates. Australia has two primary datums:

  • GDA2020 (Geocentric Datum of Australia 2020) — The current national datum, aligned with global GNSS coordinates. Coordinates on GDA2020 differ from GDA94 by approximately 1.5 to 1.8 metres.
  • GDA94 (Geocentric Datum of Australia 1994) — The previous national datum, still referenced by many existing survey marks and legacy datasets.

In Benchmrk, the point details panel indicates which datum a mark's coordinates reference. Some jurisdictions are transitioning from GDA94 to GDA2020, so you may see marks with coordinates on either datum. The datum field is important for ensuring coordinate accuracy in professional work.

Horizontal/Vertical Class​

A classification system that indicates the accuracy of a survey mark's coordinates:

  • Horizontal Class — Rates the positional accuracy of the mark's horizontal coordinates (latitude/longitude or easting/northing). Classes range from high precision (Class A, suitable for geodetic control) to lower precision (Class D, suitable for general mapping).
  • Vertical Class — Rates the accuracy of the mark's height/elevation. Similar classification scale from high to low precision.

In Benchmrk, horizontal and vertical class values appear in the point details panel for each survey mark. These classifications help you assess whether a mark's accuracy is sufficient for your project requirements. The AI Assist preferences allow you to set minimum horizontal and vertical class thresholds when searching for marks.

Latitude/Longitude​

Geographic coordinates that specify a location on the Earth's surface using angular measurements:

  • Latitude — The angle north or south of the equator, ranging from -90° (South Pole) to +90° (North Pole). All Australian survey marks have negative latitude values (southern hemisphere).
  • Longitude — The angle east or west of the Prime Meridian, ranging from -180° to +180°. Australian marks typically fall between 113° and 154° East.

In Benchmrk, latitude and longitude are displayed in decimal degrees in the point details panel and are the input format for coordinate searches. The map itself uses latitude/longitude for positioning, and the fly-to tutorial actions accept lat/lng parameters.

Map Grid of Australia (MGA)​

The official map projection system for Australia, based on the Universal Transverse Mercator (UTM) projection applied to the Australian Geodetic Datum. Australia is divided into UTM zones (numbered 49 through 56), each 6° of longitude wide. MGA provides Easting/Northing coordinates in metres, which are more practical for local measurements than angular latitude/longitude values.

In Benchmrk, the point details panel shows MGA zone and projected coordinates for survey marks. The zone number (e.g. MGA Zone 56 for the Sydney region) tells you which strip of the projection the mark falls in. MGA2020 refers to MGA coordinates on the GDA2020 datum; MGA94 refers to coordinates on the older GDA94 datum.

Permanent Survey Mark (PSM)​

A survey mark intended for long-term use, typically a metal pin, plaque, or disc set in concrete or bedrock. PSMs are established by state survey authorities and form part of the geodetic control network. They are designed to be stable and durable, surviving for decades. In Benchmrk, PSMs appear as a specific mark type with their own symbology in the Layer Manager. The point details panel shows PSM-specific metadata including the mark's physical description, condition, and establishment date.

Survey Control​

The network of survey marks with precisely known coordinates that serves as the spatial reference framework for all other surveying and mapping work. Survey control points are established through high-accuracy geodetic observations and form a hierarchy from national-level primary control down to local secondary and tertiary marks. In Benchmrk, all displayed marks are part of the survey control network for their respective jurisdictions. The Horizontal/Vertical Class values indicate where each mark sits in the accuracy hierarchy.

Traverse​

A surveying method where a series of connected lines are measured between survey marks to determine their relative positions. A traverse involves measuring distances and angles between consecutive points along a path. Traverse networks are a fundamental technique for establishing Survey Control and are referenced in mark metadata when the mark was established or verified through traverse observations. In Benchmrk, you may see traverse references in a mark's establishment history or survey plan details within the point details panel.

Trigonometric Station​

A survey mark established on a high point (hilltop, tower, or elevated structure) specifically for triangulation and trigonometric surveying. These stations were historically used to build geodetic control networks by measuring angles between visible stations. Trigonometric stations (often abbreviated as "Trig Stations" or "TS" in mark identifiers) are a common mark type in Benchmrk. They appear with their own symbology in the Layer Manager, and their point details include the station's elevation, observation history, and physical description.

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