The Spatial Space

what’s the difference?

Projections

A map projection refers to the process of representing the three-dimensional surface of the Earth on a two-dimensional map. Since the Earth is a sphere (or more accurately, an oblate spheroid), it is impossible to accurately represent its surface on a flat surface without some form of distortion.

Map projections use mathematical formulas to transform the Earth’s curved surface onto a flat map. There are various types of map projections, each with its own set of characteristics and distortions.

Some common types include the Mercator projection, the Robinson projection, the Conic projection, and the Azimuthal projection.

The choice of map projection depends on the purpose of the map and the area being represented. Different projections are optimised for specific uses, such as preserving area, shape, direction, or distance. Each projection introduces some level of distortion, and cartographers need to consider which distortions are acceptable for their specific mapping needs.

Coordinate systems

A coordinate system is a reference framework used to define and locate points on the Earth’s surface. It is a mathematical system that assigns numerical values to points based on their spatial positions.

The most commonly used coordinate system is the geographic coordinate system, which uses latitude and longitude to specify locations on the Earth’s surface.

Latitude measures the distance north or south of the Equator, while longitude measures the distance east or west of the Prime Meridian. By combining latitude and longitude values, you can determine a unique point on the Earth’s surface.

Other coordinate systems, such as the Universal Transverse Mercator (UTM) system, use a grid system of easting and northing coordinates to represent locations.

Common projections

1. Mercator Projection: This is one of the most well-known and widely used projections. It preserves accurate angles and shapes but distorts areas as you move away from the equator. It is often used for navigational purposes and for mapping regions near the equator.
2. Robinson Projection: The Robinson projection aims to create a visually pleasing map by balancing distortions across the entire map. It provides a compromise between shape, area, distance, and direction. This projection is frequently used in world maps and thematic maps.
3. Conic Projection: Conic projections are created by projecting the Earth’s surface onto a cone. They are typically used for mapping mid-latitude regions. Examples of conic projections include the Albers Equal Area Conic Projection, which preserves areas accurately, and the Lambert Conformal Conic Projection, which preserves both shape and angles.
4. Azimuthal Projection: Azimuthal projections project the Earth’s surface onto a plane from a specific point. They preserve distances and directions from that central point, making them useful for mapping polar regions. The Lambert Azimuthal Equal Area Projection and the Stereographic Projection are examples of azimuthal projections.
5. Gall-Peters Projection: The Gall-Peters projection, also known as the Peters projection, aims to provide an equal-area representation of the Earth’s surface. It accurately represents the relative sizes of landmasses, but shapes are significantly distorted, particularly towards the poles. This projection is often used to emphasise social, political, and development issues.
6. Winkel Tripel Projection: The Winkel Tripel projection is a compromise projection that attempts to balance distortions in size, shape, and distance. It is commonly used for world maps and strikes a balance between visual appeal and accuracy.

coordinate reference systems (crs)

A Coordinate Reference System (CRS) is a framework used in cartography, geographic information systems (GIS), and spatial data analysis to accurately represent and reference locations on the Earth’s surface. It provides a standardised system for defining and describing spatial data, allowing for consistent measurement, analysis, and visualisation of geographic information.

The Earth is a three-dimensional object, and representing its curved surface on a flat map introduces distortions. CRS helps address this challenge by establishing a reference framework that defines how coordinates are assigned to specific locations on the Earth’s surface.

CRSs consist of two main components: the coordinate system and the datum.

The coordinate system is a mathematical model that defines how positions are measured and represented. It can be based on geographic coordinates (latitude and longitude) or a grid system (easting and northing coordinates). The choice of coordinate system depends on the nature of the data and the purpose of the analysis.

The datum is a reference surface or model used to anchor the coordinate system to the Earth’s surface. It provides a set of control points and parameters that align the coordinate system with the physical Earth. Common datums include WGS84 (World Geodetic System 1984) and NAD83 (North American Datum 1983).

CRSs can be categorised into two types: geographic CRS and projected CRS.

Geographic CRS (also known as geodetic CRS) uses latitude and longitude to define positions on a curved surface. It is suitable for global analysis and representation.

Projected CRS, on the other hand, transforms the curved surface of the Earth onto a flat plane using map projections. It is used for localised analysis and mapping.

CRSs also define the units of measurement for coordinates, such as decimal degrees, meters, or feet, depending on the specific CRS being used.

Choosing the appropriate CRS is essential for accurate spatial analysis, data integration, and interoperability. It ensures that spatial data from different sources align properly and can be analysed and visualised together.

common CRS’

1. WGS84 (World Geodetic System 1984):
   • Description: A global geographic CRS widely used for GPS and satellite imagery.
   • Type: Geographic CRS
   • Units: Decimal degrees (latitude and longitude)
2. UTM (Universal Transverse Mercator):
   • Description: Divides the Earth into zones for accurate regional mapping.
   • Type: Projected CRS
   • Units: Meters (easting and northing)
3. Web Mercator (EPSG:3857):
   • Description: Designed for web mapping services like Google Maps.
   • Type: Projected CRS
   • Units: Meters
4. NAD83 (North American Datum 1983):
   • Description: Commonly used in North America for various mapping applications.
   • Type: Geographic CRS
   • Units: Decimal degrees (latitude and longitude)
5. EPSG:4326 (European Petroleum Survey Group 4326):
   • Description: A widely used geographic CRS based on WGS84.
   • Type: Geographic CRS
   • Units: Decimal degrees (latitude and longitude)
6. EPSG:27700 (British National Grid):
   • Description: A projected CRS used in Great Britain for mapping and surveying.
   • Type: Projected CRS
   • Units: Meters (easting and northing)
7. EPSG:32633 (WGS 84 / UTM Zone 33N):
   • Description: UTM zone 33 in the northern hemisphere.
   • Type: Projected CRS
   • Units: Meters (easting and northing)
8. EPSG:3395 (World Mercator):
   • Description: A cylindrical projection used for global maps.
   • Type: Projected CRS
   • Units: Meters
9. EPSG:3035 (ETRS89 / LAEA Europe):
   • Description: A Europe-centric equal area projection.
   • Type: Projected CRS
   • Units: Meters
10. EPSG:3857 (Popular Web Mercator):
    • Description: A widely used web mapping CRS for online services.
    • Type: Projected CRS
    • Units: Meters
11. EPSG:2154 (RGF93 / Lambert-93):
    • Description: Used in France for various mapping applications.
    • Type: Projected CRS
    • Units: Meters
12. EPSG:23030 (ED50 / UTM Zone 30N):
    • Description: UTM zone 30 in the northern hemisphere based on ED50.
    • Type: Projected CRS
    • Units: Meters (easting and northing)

summary

Coordinate Systems: Coordinate systems are mathematical frameworks used to represent and locate points in space. They define a set of coordinates that specify the position of a point relative to a reference point or origin.

CRS (Coordinate Reference System): A Coordinate Reference System is a framework that combines a coordinate system with a datum, providing a standardized way to reference and represent spatial data. CRSs ensure that spatial data aligns properly and can be analyzed, integrated, and visualized accurately.

Projections: Projections are mathematical transformations used to represent the curved surface of the Earth on a flat map. Due to the Earth’s spherical shape, distortions occur when projecting it onto a 2D surface. Projections aim to balance and minimize these distortions based on specific properties like area, shape, distance, or direction.

In summary, coordinate systems define how points are located in space, CRSs combine coordinate systems with datums to reference spatial data, and projections transform the Earth’s curved surface onto a flat map while managing distortions. These concepts are essential for accurately representing and analyzing geographic data in various applications.