In the first part of our blog post titl! “Geographic and Project! Coordinate Systems” we explain! coordinate systems and their types. In this part we will discuss how coordinate systems are assign!. You can access the previous part of the series from the link below:
Part One
Coordinate System Assignment
You can view the details of any coordinate system in ArcGIS Pro by clicking the Details button mark! in green in the image below on the Coordinate Systems tab in the Map Properties window.
The following image shows the Details page of the Fuller (world) coordinate system:
The first line says it is a Project! Coordinate System
A project! coordinate system, by definition, requires a projection. The second row shows that this coordinate system uses the Fuller projection, invent! by Buckminster Fuller in 1954.
WKID is a unique identifying number for the project! coordinate system.
In a project! coordinate system, coordinates are usually stor! in linear units such as meters.
False Easting , digitization opens the way to new markets more smoothly False Northing and Option parameters are for Fuller projection. Other projections have parameters like Central Meridian , Standard Parallel and Latitude of Origin . You should use these parameters if you want to align the project! coordinate system at a specific point. The following image shows two different project! coordinate systems, Hawaii Albers Equal Area Conic and Canada Albers Equal Area Conic . Both use the same projection but have different projection parameters.
WKID is also valid for geographic coordinate systems
In a geographic my 10 google ads tricks to rock your campaigns coordinate system, coordinates are usually stor! in angular units such as degrees.
The prime meridian is a line of longitude defin! as 0. Greenwich, England, is usually us!.
Datum defines what model is us! to alb directory represent the earth’s surface and where that model is plac! in relation to the surface.
The spheroid is the regular model of the irregular earth and is part of the datum.
Can’t we choose a geographic coordinate system instead of a projection coordinate system for our map? You may have made maps in WGS 1984 before and seen that it was drawn without any problems.
Shall we try it together?
In the Map Properties window, expand the Geographic Coordinate System list and select any one and click the OK button .
Your map will look like this, regardless of which geographic coordinate system you choose:
Remember that it is impossible to draw the round earth on a flat surface without projection. So when you tell ArcGIS to display this map as a flat map on your screens by selecting a geographic coordinate system, it has to choose a projection! So it applies a fake “Plate Carrée” projection. This projection is just a grid system consisting of a simple latitude-longitude representation. It is measur! in angular units (degrees) instead of linear units (meters). This projection is easy to understand and calculate, but it also distorts all areas, angles and distances. Therefore, it is not correct to use it for analysis and measurement, the project! coordinate system should be select!.
In summary;
You can store your data in a geographic coordinate system, but you can’t plot it on a flat map without using a project! coordinate system.
The geographic coordinate system determines where the data will be plott!. The project! coordinate system describes how the geographic coordinate system will be drawn flat on the map.
Which geographic coordinate system you choose depends on where you are mapping.
Which project! coordinate system you use depends on where you are mapping and also on the nature of your map. For example, should you distort space to preserve angles or vice versa?