Coordinate Systems and Projections

Introduction:

Map projections allow for systematic transformations that allow accurate representations of the Earth's surface on a flat surface. In order to accurately place data on a map, coordinate systems were created in order to give references and ensure accurate information. Since the Earth's shape is not perfectly round, it is an ellipsoid, GIS can be used to collect accurate data. These geographic coordinate systems use a 3D model to name points on the surface of the earth which are then paired with its relative geographic coordinate system. Geographic coordinate systems are then paired with projected coordinate systems in order to turn the Earth's spherical shape to a flat map. In this lab, we used these concepts in ArcGIS Pro alongside the Esri tutorial 'Introduction to Coordinate Systems' to better understand how projections and coordinate systems work.

Objectives:

#1: Discover, identify, and apply basic concepts behind projections and coordinate systems.

#2: Recognize, relate, and compare geographic and projected coordinate systems using ArcGIS Pro software

#3: Demonstrate proficiency and knowledge on how to effectively use projections and coordinate systems that fit the need.

#4: Demonstrate proficiency and knowledge on how to effectively work with projections and coordinate systems in ArcGIS Pro software.

Methods/Assignment (Part1):

The first part of this training exercise had us open a map and zoom in to Long Island, New York in order to view more detail. We then enabled the WGS 1984 layer to turn it on (Figure.1) From here we used the swipe tool to examine the differences. However, there is not enough detail to clearly see the difference between the layers. As you can see in the figure below, it is impossible to tell the difference between the layers.

(Figure.1 Long Island WGS84 Swipe Tool)

To get a better understanding of how large of a difference there can be, we zoomed in to detail 1,2, and 3. By enabling all 3 spheroids (WGS84, International 1924, and Clarke 1866) the difference can be clearly seen. From the images below (Figures. 2-4) the various colors represent the three spheroids and their differences.

(Figure.2 Detail 1)

(Figure.3 Detail 2)

(Figure.4 Detail 3)

By using the measure tool, the difference between the Clarke 1866 and WGS84 spheroids were measured showing a difference of roughly 240 meters. This difference can be a huge issue when analyzing data. Using the wrong spheroid when conducting an analysis of UAS data can throw off the results an immense amount and result in useless information. Using the right spheroid will ensure accurate and efficient data. For example, if the individual who collected the data used WGS84 and set a point at a specific coordinate location and the individual who is analyzing the data uses Clarke 1866, the point would be off by 240 meters which can throw off the entire set of data.

Methods/Assignment (Part2):

The next section of the training exercise consisted of us analyzing specific points on the map to understand geographic coordinate systems. These points are cities all over Africa and in order to analyze these points in respect to geographic coordinate systems we used a feature layer. By taking the coordinates (latitude and longitude) from the table provided, we plugged it into the feature layer and made sure to select the correct coordinate system.(Figure.5)

(Figure.5 Coordinate Table)

After inserting the information into the feature layer and setting up symbols for each point, the cities in Africa displayed on the map in their respective locations. (Figure.6) This worked perfectly but to better understand the concepts we inserted data that was missing it's spatial reference. Upon running the feature layer, the points ended up in the completely wrong location near the equator. (Figure.7) In order to accurately display information, it is crucial that the data that identifies the coordinates system is present. 

(Figure.6 Cities in Africa Displayed Correctly)

(Figure.7 Cities in Africa Missing Spatial Reference)

The reason these points are in the incorrect location is due to the fact that they have no spatial reference information. Because of this, the program assumes that all of their origins are at the coordinates 0,0. 
By defining the coordinate system as WGS1984, the points move to their correct locations, aligning with the green points shown in figure 6. (Figure.8)

(Figure.8 Correct Coordinate System)

Discussion:

Understanding projections is crucial in analyzing UAS data to ensure that the results are accurate and minimize error. As seen in this lab, the amount of error caused by the wrong projection can be immense and ruin the results of all the data. In this lab we explored, using an Esri exercise, how to adjust, analyze, and understand different projections and how they can effect UAS data. Below is the certificate received for completing the course.