Projected Coordinate Systems

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 Today is a blog post on Coordinate Systems!

There are two main types of coordinate systems: 

Geographic (GCS) and Projected (PCS)

We simply want to take data mapped in our world (3D) and lay it on a flat map. This is called projecting it into 2D. A GCS is where the data is located and a PCS is how to draw that 3D data on a flat map. I would think of a GCS a globe, while a PCS is a flat rectangular map you see in a textbook. However, when we project Geospatial data onto a flat surface, there will be distorted data such as the shape, size, area, direction or angle of the object being projected. 

This is why it is crucial to understand the different kinds of coordinate systems to accurately portray your data on your map. The ones I will be showing you below are Conical Projected Coordinate Systems and are great for doing world maps. These would not be great to use for using local maps for states, counties, or cities. 

https://www.esri.com/arcgis-blog/products/arcgis-pro/mapping/gcs_vs_pcs/

https://pro.arcgis.com/en/pro app/latest/help/mapping/properties/coordinate-systems-and-projections.htm




Here are some examples of Projected Coordinate Systems Below:

Pay close attention to the circles are how they become distorted in the maps below...


Robinson Projection

In the Robinson world projection, we can immediately identify from the map below that the world is being displayed with little distortion than that of the Mercator projection. This projection is unique simply since it is not conformal or equal area. It distorts shapes of objects, size, distance, angles, and even directions of objects. However, it is a great projection for displaying the entire world. Anything beside the world it would not be recommended to use. This projection was unique in that it did not derive from geometric equations or mathematical formulas to create the projection. 

Patterson Projection

This projection is a cylindric projection and the meridians in the map below are equally spaced straight lines. This projection still has a large degree of distortion regarding direction, shape, angles, size, and distance. However, this projection has less distortion than a lot of cylindric projections and can portray the world on a rectangular map rather well. The Patterson projection does preserve the shape of land masses better than most projections and makes for a great world projection, even though there is still a lot of distortion occurring in the map near the north and south poles (the circles are different in size but as you can see about the Mercator projection, the differences in the circle size are much smaller from the poles to the Equator). 
Natural Earth Projection

This projection is very similar to the ones displayed above, having distortion is shape, angles, direction, distance, and area since it is a pseudo cylindrical projection. The distortion increases as the latitude changes (not latitude just like the map projections above). The distortion can be seen below with the changes in the circle size and shape near the poles (latitude areas). 

Mercator Projection

According to (Brewer, 2016) the distance and area distortion on the Mercator projection increases severely toward the poles. The Mercator projection preserves the angles of objects and feature classes in a projection. However, it does not preserve the size of an object. As the distance from the Equator to the Poles increases, the land is more distorted showing large land masses near the South Pole and North Pole (Antarctica for example) and smaller land masses near the equator. 


So, the Mercator projection does not accurately display the actual size or mass of the Earth’s most northern and southern latitudes showing large landmasses that are not accurate to size. It will still show that a circle is a circle, but that the circle is much larger than a circle near the Equator. Africa is one of the largest continents in the world. Yet in the Mercator projection, Europe and Greenland look substantially large and Africa looks like one of the smallest continents in the world.


Did you know that in most school textbooks Mercator is used for World maps? 

This means we are teaching our youth that countries are the same size across the world and providing inaccurate sizes. Africa is 14 times larger than Greenland in the Mercator map above. Yet the map shows Africa the same size as Greenland? 


I think its time to update some geography books...


Here is another example of a Projected Coordinate system for Canada:

Map of Canada using the Lambert Conformal Conic Projection

In the map below, I created a map of Quebec, Canada, in which I used the NAD 1983 Quebec Albers Coordinate system 


§  Geodetic Datum

The Datum is North American 1983 (CRCS) which uses the 180 spheroid from the Geodetic Reference System. This is very similar to the WGS 1984 spheroid in which the datum is earth-centered, or the earth is the center mass of the datum.

§  Family 

The family is a Conic projected coordinate system which uses two standard parallels with the 1/6 rule to determine the latitude ranges for the coordinate system.

§  Type 

The type is an Albers type Coordinate system which means the projected coordinate system uses equal area of distortion to project areas or land masses that need equal area size and shape. This a great type for a country in which the area is so closely accurate and direction is mostly accurate, and the distortion lies mainly in the distance and scale. 


Below is a map of the State of Georgia
The coordinate system used is NAD 1983 Georgia Statewide Lambert U.S. Feet



I decided to choose the state of Georgia since it is where I live, where I was born, and where I currently map GIS data for Clarke County regarding the Athens-Clarke County Police Department (ACCPD). I am very passionate about making Georgia a better and safer community, which is why I work as a GIS Crime Analyst for the ACCPD. 

The reason for choosing the NAD 1983 Georgia statewide Lambert (U.S. Feet) is because the state of Georgia falls within two state plane coordinate systems, East, and West. The state also falls within two UTM zones, 17N and 16N. Therefore, I used a custom system for the state of Georgia under the state systems projected coordinate systems section in Arc GIS Pro. I feel as if NAD 1983 is more accurate than NAD 1927 due to recent updates in the projection using the 1983 spheroid. 


Feel free to check out the video below on Projections and Coordinate Systems by Esri!

Things to continue to research following this blog post would be understanding the following:
 Datums
Albers vs. Lambert 
Conic vs. planar

See you next time!



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