Our planet is neither flat nor perfectly round or spherical. Planet Earth has no regular geometric shape and is called a geoid1
. The shape of the Earth approximates an ellipsoid as a result of rotation about its minor axis.
1A geoid is a mathematical representation of the Earth calculated using only the Earth’s gravity and rotation, and no other influences such as wind or tides.
The Earth’s surface can differ significantly from the geoid in many places. So some tricks are needed to make the calculation more accurate. Use a reference ellipsoid that matches the geoid over only some part of the surface.
Today, the most popular Earth ellipsoid and its associated earth coordinate system is WGS84.
Measurements of objects placed on the Earth will always be subject to some degree of inaccuracy. There has been and will continue to be a lot of discussion about how to calculate areas and objects on the maps and which SRS to use to get more accurate land measurement.
Currently, the most accurate and least distorted way to calculate area is using a map projection. Note that map projections are not yet perfectly accurate representations of the Earth.
Each projection has its distortions of angular fit, distance, and area. It will always be a compromise between combining multiple properties or being a distortion of all properties of an area, distance, and angular fit within some acceptable limit. Additionally, all the actual measurements are approximate. There is no such thing as “the” area of a region of the Earth’s surface area.
Cartographers have developed map projections that project the Earth onto a flat surface with acceptable accuracy. The most popular projection and coordinate system in GIS is the UTM (Universal Transverse Mercator). UTM is used to create topographic maps and build natural resource databases because it provides accurate measurements in the metric system used by most countries and throughout the scientific community. Cartographic information is more than metric parameter coordinates, it also uses attribute2
information as indicators of thematic and temporal features.
2An attribute is basic data that describe the properties of the elements of your model. Attributes are symbols (names), numbers (statistical features), and graphic features (color, structure of contours, etc.).
You can use our library to calculate land area, island area, state area, or any area on the map. Use the Equal Area Projection3
to calculate area to maintain the proportionality of the areas of objects.
3Equal area projection preserves the proportionality of the areas of objects. So if the area of one object on Earth is twice the area of another object, the image of the first area will also be twice the size of this second image on the projection. However, the equal-area projections do not preserve shape similarity. A round island appears in the projection as an ellipse of equal area.
So how to calculate the area of Russia, Greenland, or one of the USA states?
First you need to search and download a map of the object you want to measure. You can download various maps from free sources. Map data is mostly available in WGS84, Web Mercator, or UTM projections which already have many distortions and are not accurate enough for a land measurement.
To correctly calculate the area of an object, the map must be converted from a stored projection to an equal area projection. For example, to find the area of a country, you can try using the Lambert Azimuthal Equal Area projection.
Russia is the largest country in the world by area so what do we need to make sure of this?
Among all the available options, EPSG:3576 is the best choice in Russian Map EPSG Codes. The advantage of this projection is that the Krasnoyarsk Krai and Northern Russia are less distorted. The downside is that you can’t visualize the entire world map but Russia and adjoining regions only. Below is the sample code for conversion. This code shows the conversion to the selected projection and the calculation of the area of the object.
Which map projection and coordinate system to use depends on the extent of the area you are working with, the analysis you are performing, and often data availability.
Countries actually have three different measures of area: land area (the area of all the land), total land (the country’s land area, lakes, reservoirs, inland rivers, and sometimes coasts and territorial waters), and water area (inland waters).
So there are three dimensions:
- Total area: the sum of land and water areas within international boundaries and coastlines.
- Land area: the sum of all land areas within international boundaries and coastlines, excluding water area.
- Water area: the sum of all inland water areas (lakes, reservoirs, and rivers) within international boundaries and coastlines. May include coastal inland waters. Unless otherwise specified, territorial waters are not included.
National claims to parts of Antarctica are not included.
|Country||Land Area (km2)||Water Area (km2)||Total Area (km2)|
The Lambert equal area projection is well suited for mapping land areas that have a symmetrically proportional shape, for entire countries or islands, such as Ukraine, Greenland, or Australia, and smaller objects, such as fields, the backyard of your house, or a land allotment of several acres. Make sure you use the EPSG code most appropriate for your region.
SRS (Spatial Reference System) or CRS (Coordinate System) is a coordinate-based local, regional, or global system used to determine the location of geographic features. An SRS defines a particular map projection, as well as transformations between different spatial reference systems. SRS can be referenced by an integer SRID, including the EPSG codes defined by the International Oil and Gas Producers Association.
If you have any questions, you can post a question on our forum