Coordinate Reference Systems (CRS) and Geodetic Datums: What’s the difference?

Coordinate Reference Systems (CRS) and Geodetic Datums: What’s the difference?

Coordinate Reference Systems (CRS) and geodetic datums are both used to represent the Earth’s surface, but they are different concepts, and importantly, serve different purposes. We provide definitions, highlight their differences and considerations for practical applications.

Coordinate Reference System (CRS)

A CRS is a coordinate-based system that provides a standardised framework for describing and locating points on the Earth’s surface. CRS is primarily used to represent specific locations on the Earth’s surface with precision and consistency.

A CRS can also be referred to as a spatial reference system (SRS) in many cases.

It defines a set of coordinates that can be used to represent the location of a point on the Earth’s surface.

A CRS typically includes a reference point (an origin), a set of axes (coordinate axes), and a unit of measurement (such as metres).

Geodetic Datum

A geodetic datum, on the other hand, is a mathematical model that defines the shape and size of the Earth’s surface, as well as the location of a reference point (the geodetic origin) and the orientation of the axes.

A geodetic datum provides the framework for measuring and comparing positions on the Earth’s surface.

It includes parameters describing the Earth’s ellipsoidal shape (semi-major and semi-minor axes), the flattening of the Earth, and the position of the datum origin.

Geodetic datums are essential for achieving high accuracy in geospatial measurements, especially over large areas.

What’s the difference?

While a CRS and a geodetic datum both provide frameworks for representing the Earth’s surface, they are different in their scope and purpose.

They serve distinct purposes in spatial representation and measurement.

The main differences between Coordinate Reference Systems and Geodetic Datums

Coordinate Reference Systems (CRS)Geodetic Datums
USESA CRS is used to represent the location of a point on the Earth's surfaceA geodetic datum is used to define the shape and size of the Earth's surface and the reference point used to measure positions
PRIMARY FOCUSA CRS deals primarily with coordinate systemA geodetic datum deals with the underlying shape and size of the Earth's reference ellipsoid
DEFINITIONSCRS definitions typically remain consistentGeodetic datums may evolve over time due to improvements in measurement techniques and advancements in geodesy
OPTIONSMultiple CRS are availableMultiple geodetic datums are available

It’s important to note that in many cases, CRSs are defined based on specific geodetic datums, ensuring compatibility and accuracy in spatial representations.

For example, the UTM system uses the WGS84 geodetic datum.

The decision between which CRS or geodetic datum to use

There are multiple choices of both CRS and geodetic datums available for users to select from.

The choice of CRS and geodetic datum depends on various factors such as the geographic region, application, and desired level of accuracy.

Geographic Region

Geographic Region

Different regions of the world may use specific CRS and geodetic datum combinations that are optimised for that region’s geographical characteristics.

Learn about the geodetic datums we use and reference in Australia.

Applications

Application

The type of application you’re working on can influence your choice of CRS and geodetic datum.

For example, surveying and mapping applications often require high accuracy, so a CRS and geodetic datum that offer precision are chosen. On the other hand, less accurate CRS and datum choices may be suitable for applications like general-purpose Geographic Information Systems or web mapping.

Accuracy

Desired Level of Accuracy

The level of precision required for a particular project or task is a crucial deciding factor. Some CRS and geodetic datum combinations are designed to provide centimetre-level accuracy, while others may provide accuracy at the metre or even decimetre level. So the choice really depends on the project’s specific accuracy requirements.

In practice, these above factors need to be carefully considered to ensure users choose the CRS and geodetic datum that is appropriate and aligns to their needs.

Considerations include whether it accurately represents geospatial data, can be integrated seamlessly with other data sources or used in specific analysis or modeling purposes. This will help avoid errors and inconsistencies in geospatial data handling and analysis.

Practical uses for CRS and geodetic datums

In practical terms, when working with geospatial data and mapping, you often need to specify both the CRS and the geodetic datum to ensure accurate and consistent spatial referencing and calculations. Keep in mind different geographic regions and applications may use specific datums and CRS to meet their needs, so understanding the distinction between them is essential for accurate geospatial referencing and analysis.

How to set these in Snowflake

If using a Geography data type the CRS used is WGS 84 and cannot be changed.

If using the Geometry data type, the CRS (or SRS) can be set with the ST_SETSRID function. To change the CRS of a geometry, use the ST_TRANSFORM function.

SELECT
ST_TRANSFORM(
ST_GEOMFROMWKT('POINT(389866.35 5819003.03)', 32633),
3857
) AS transformed_geom;

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What is a Coordinate Reference System (CRS)?

What is a Coordinate Reference System (CRS)?

Imagine you’re a contestant on The Amazing Race or on a much smaller scale, playing treasure hunt, and are referencing a giant map. The map is the Earth, and you need to find specific locations. Now, to make sure you can find the next pit stop or treasures accurately, you need a set of rules for reading and describing locations on the map.

That set of rules is like a Coordinate Reference System (CRS).

A CRS defines how to assign coordinates (such as X and Y on a grid) to places on the map.

When there is a consistent way to find places on a map, everyone uses the same method to describe locations accurately.

Coordinate Reference System (CRS)

A Coordinate Reference System (CRS) is a system that uses numbers to precisely pinpoint locations on maps or the Earth’s surface, ensuring everyone uses the same rules for describing positions.

By defining sets of coordinates and a standardised framework, it offers a consistent way to specify locations, making it possible for maps and geographic data to be accurately interpreted and shared.

A CRS typically includes a reference point, a set of axes, and a unit of measurement.

What Purpose Does a CRS Serve?

CRS is primarily used to describe how coordinates are represented, mapped, and interpreted in a specific geographic or projected space. It is used for locating and referencing points on the Earth’s surface accurately.

CRS is used in geography (the study of the Earth’s landscapes, environments, places, and the relationships between people and their surroundings) and cartography (the design, production, and interpretation of maps, which are graphical representations of geographical information).

Different Types of CRS

  • Geographic CRS: Based on a spherical or ellipsoidal model of the Earth’s surface, commonly using latitude and longitude coordinates.
  • Projected CRS: Maps the three-dimensional spherical or ellipsoidal Earth onto a two-dimensional plane, such as a map or a flat surface. Examples include Universal Transverse Mercator (UTM) and State Plane Coordinate Systems.
  • Vertical CRS: Specifies elevations or depths relative to a reference surface (e.g., sea level).

Some examples of commonly used CRS include:

How CRS is Used in Property and Real Estate

Coordinate Reference Systems (CRS) play a crucial role in property and real estate in several ways:

  • Property Identification:
    CRS can be used to precisely locate and identify properties. Property boundaries, corners, and specific locations can be accurately described using coordinates, which is essential for legal and cadastral (land ownership) records.
  • Mapping and Surveying:
    Surveyors use CRS to create property surveys and maps. These maps are crucial for property transactions, boundary disputes, and construction projects. Accurate coordinates ensure that properties are properly defined.
  • Land Registration:
    When properties are bought or sold, accurate coordinates and CRS are used to update land registration records. This helps ensure the legality of property transactions and reduces the likelihood of property disputes.
  • Zoning and Planning:
    Urban and regional planners use CRS to map out zoning areas, plan infrastructure, and make decisions about land use. This information is crucial for developers, homeowners, and local governments.
  • Property Valuation:
    CRS can be used in property valuation models to assess the value of properties based on their location, proximity to amenities, and other geographic factors.
  • Real Estate Marketing:
    Real estate agents and online platforms often use mapping systems that rely on CRS to display property locations accurately. This makes it easier for buyers to understand the property’s surroundings.
  • Environmental Impact Assessment:
    When considering property development, CRS can be used to assess the potential environmental impact, taking into account factors like proximity to water bodies, floodplains, and protected areas.
  • Infrastructure Development:
    CRS is used in the planning and construction of transportation networks, utilities, and other infrastructure. It helps ensure that developments are located optimally and adhere to safety standards.
  • Disaster Risk Assessment:
    CRS is also essential in assessing properties’ vulnerability to natural disasters, such as floods or earthquakes. This information is vital for insurance purposes and disaster preparedness.

As you can see Coordinate Reference Systems (CRS) play a pivotal role in many facets of property and real estate management, and are used widely by proptechs.

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