Introduction to Coordinate Systems and Projections

 

Figure 1: ESRI Coordinate Systems Tutorial

Introduction to Coordinate Systems:

For this lab we were tasked with completing an online ESRI course that covered some of the basics of different projections and coordinate systems. The tutorial gave us a data set to use with ArcGIS, but could theoretically be used with different software's. The Tutorials main focus was more on the GIS side, with less of a focus on UAS. However, GIS is one of the largest applications of UAS, so understanding how this all works is important if you are looking into a career in UAS.

For this blog we will be looking more into different projections and the types of coordinate systems. While we used ArcGIS for this lab assignment, I will not be going into detail on that software, as it has been covered multiple times on this blog.

Tutorial Link: https://www.esri.com/training/catalog/5d8258be55cf937306d3bd63/introduction-to-coordinate-systems/ 

Methods:

Firstly, let's cover the two basic types of coordinate systems that are used for mapping:

• Geographic Coordinate Systems:
• These are based on the location of points on a glove. As such they are more accurate than projections on a flat surface, but are not as easy to display in a two dimensional format. These types of projections are better for large-scale operations as points are true to their location. Points are measured in latitude and longitude, with points being written with degrees, minutes, and seconds.
• Projected Coordinate Systems:
• These projections are based on two dimensional displays. Since you are displaying a three dimensional object (In most cases the Earth) in a two dimensional format, they are going to be issues. The main issue caused is different forms of distortion, which depending on the type of projection you are using will lead to a certain criteria displayed improperly. Locations on these types of projections are measured on a linear scale, such as with meters or feet.

Projections:

Now we will be covering the different kinds of projections that were covered in the ESRI tutorial. I will be using the images supplied by the tutorial for this post, all credit to ESRI for these images.

When choosing a projection, you have to decide what spatial properties you would like to preserve.

When developing a projection, you choose a surface that the three dimensional map is projected onto, most commonly they are; cylinders, cones, or planes. There are more complex developable surfaces, but we do not need to cover them here.

Types of spatial properties:

• Distance
• Direction
• Scale (or Shape)
• Area

Note: If a map preserves two spatial properties, one of them is always direction

Figure 2: Conformal Projection

Conformal projection will look the most familiar to the average individual. Most maps you see use this type of projection, as conformal projections aim to preserve the features or shape of objects being displayed. The Mercator projection is the most prominent example of this.

Figure 3: Equal Area Projection

Equal area projections preserve area as the name implies. By maintaining relative areas, there is distortions in the shape of objects, as shown above. These projections are useful when relative size and area of the map is important, such as when displaying continents for thematic mapping.

Figure 4: Equidistant Projection

Equidistant projections maintain accurate distances between features. They are maintained between points, meaning that there is a constant scale on the projection. Size and shape are distorted in these projections, as they are not conformal or equal-area.

Figure 5: Azimuthal Projection

Azimuthal, or true direction projections, maintain direction. The directions come from a central point, and depending on the type of azimuthal projection can also be equal area, conformal, or equidistant.

Figure 6: Gnomonic Projection

Gnomonic projections are similar to azimuthal directions, but with displaying circles as straight lines, with a central point that the map branches from. In these projections directions are true from the center point.

Figure 7: Compromise Projection

Compromise projections do not preserve any of the spatial properties, but they are made to balance out distortions in the spatial properties.

Conclusion:

Knowing how projections and coordinate systems work is important for UAS work, but also has a much broader variety of utilizations. Knowing which projection to use for an application is important, as if you try using the wrong projection you will not have access to a spatial property that you need. On top of this, many different GIS and UAS software utilize coordinate systems and projections for other data processing, so it is vital that you know what to use when. Below is the certificate I received for completing the ESRI tutorial that I based this blog on.

Figure 8: ESRI Certificate