# Considerations that influence a coordinate system

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02-15-2022 12:31 PM
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New Contributor

Hello Everyone!

What spatial factors and analysis and display considerations influence the choice of a coordinate system (and perhaps a map projection) to map or store data for a project area?

I am a beginning ArcPro user and I am creating my first map. This is a question my professor asked us in a lab class but I really don't understand what it means. Any interpretation would be much appreciated. Hoping to have a discussion!

Thank you very much,

6 Replies
MVP Esteemed Contributor

I think they are wanting to get you to think about what coordinate system should you use and how it may influence what you can do with it.   Geographic coordinate systems (aka, longitude, latitude) even have the influence of a datum .  Projected coordinate systems have their own units and are derived from a GCS and its influences.  Also, what type of analysis do you intend to use?  Are you just determining location?  Do you require measures of geometry (eg area, length).  Is the area really small? county-wide, state/province, continentental?  Pick your coordinate recording system?  Are professionals doing the work?  crowd-sourced?  Try explaining to a novice that the data needs to be collected in a modified transverse mercator coordinate system using the latest NAD83 realization.

In short, know what you are using, what its limitations are and how to convert one system to another.  There are books on this topic.  Start with the help files

Coordinate systems, projections, and transformations—ArcGIS Pro | Documentation

and mini courses

Choose the right projection | Learn ArcGIS

Have fun

... sort of retired...
New Contributor

Hi Dan,

Thank you for getting back to me. I'll check out those links. What exactly do you mean by "Geographic coordinate systems (aka, longitude, latitude) even have the influence of a datum"?

MVP Esteemed Contributor

longitude/latitude coordinates are referred to a "geographic coordinates"

As an example of the "have the influence of a datum"

Pre 1927 if you recorded a location -75, 45  (long, lat) it would have used a 1927 datum (eg description of Earth's shape).

in the year 2000, if you went to that exact location (-75, 45)  you wouldn't have been in the same spot as before because the "datum" used to describe Earth had changed.  You would have been a couple of hundred meters away from where you think you should be.

Conversely,  If you stood still for all those years in that location (work with me, pretend), you wouldn't have moved at all, but "where" you appeared to be based on the coordinates would change. 😉

... sort of retired...
Occasional Contributor III

That's kind of big question.  Projections take the not so round earth and project it onto a flat surface.  Some projections keep measurements/distance more accurate at the cost that the shape of represented areas my change slightly (especially larger ones).  Other projections keep the shapes of areas more accurate than others at the cost of distorting distance measurements.  Other projects preserve direction or angles or scale, so  the one you choose should be based on what's the most important aspect of the data for your purpose.  Coordinate systems are too much to talk about, but here's a good link though:

Esri Contributor

I would also have a look at the below blogs to better understand coordinate systems and why they matter. It is important to grasp the difference between geographic coordinate systems and projected coordinate systems

🙂
Esri Regular Contributor

Hi, another good resource for you might be https://learn.arcgis.com/en/projects/choose-the-right-projection/ It's a hands-on tutorial at an introductory level. It includes concepts and practical applications of the concepts--like visualizing the distortion caused by different types of projections.