Goal and Background:
- The goal of this lab is to become familiar with projected coordinate systems and geographic coordinate systems. Through this lab I have learned the difference between the two, and which projections are the appropriate ones to use based on the data displayed on the map. For example, the Wisconsin map I created has a North America 1983 geographic coordinate system. This coordinate system was chosen based on information from the metadata provided to me from the Lab 1 instructions. Following that, I chose a North American 1983 StatePlane projection with a Central Wisconsin focus as the projected coordinate system because the GIS data displayed on the map portrayed the Central Wisconsin area. These coordinate systems did not come with the shapefiles, so I had to use one of the other skills I learned from this lab and previous tutorials to adjust the projected coordinate systems to the appropriate ones so that the display of the data on the map would be accurate. Through this lab I was able to detect and resolve any projection errors within the GIS data.
Method:
- Every new map that is opened in the ArcMap starts out as
blank and all of the data I used in this lab was taken from the Lab 1 Data
folder I obtained from my instructor, this folder contains several subfolders
that store the data needed for this lab. The first step I took was adding two
shapefiles from the World folder to get a map of the world with the geogrids
shapefile displayed behind it. The next step was implementing the skills I
learned from previous tutorials to adjust the geographic coordinate system to
WGS 1984. This final step was the last one to complete my first data frame,
labeled “Geographic Projection”. To do this I found the coordinate systems tab
under properties of the Geographic Projection frame and from there I found the
WGS 1984 projection under the World subfolder of the Geographic Coordinate
System folder. Similar steps were taken
for the next four data frames, each with its own individual projected
coordinate system: Mercator, Sinusoidal, Equidistant Conic, and Robinson. Each
of these projections can be found under the World subfolder of the Projected
Coordinate Systems folder.
The next portion of this assignment asked me to work with projections at a state level, as opposed to a world level like in the previous section. This part of lab 1 began with a shapefile of the United States from the USA folder. From there I had to isolate the state of Wisconsin from the rest of the map, in order to create an entirely new shapefile of Wisconsin alone. To do so, I opened the Select by Attributes tool and entered the “STATE_NAME” = “Wisconsin” clause to isolate Wisconsin. I then created a layer from the selected features and exported those features to my lab data folder as a new shapefile for Wisconsin. After changing the projection to the “UTM, NAD 1983, Zone 16N” projection by finding the UTM folder under Projected Coordinate System, opening it to the NAD 1983 folder and selecting NAD 1983 UTM Zone 16, I had my sixth data frame completed.My seventh and final frame was a map of the United States that showed the roads that ran throughout the state of Michigan. A states shapefile and a Michigan state roads feature were added to the final data frame. The problem with this map was that the two features lined up correctly, but it was in an on-the-fly projection, meaning that certain types of analysis would not be possible with just this type of projection. That being said, I needed to change the projection of the Michigan state roads feature. To do so, I opened ArcToolbox then under the Data Management Tools I selected Projections and Transformations and then the Project tool. This allowed me to give the shapefile a different projection, without changing the geographic coordinate system. I input the Michigan feature then, I changed the output coordinate system. I found the Layers folder, and underneath it was a GCS_North_America_1983 category. I expanded that and found the states shapefile, and selected this to change the projection of the Michigan feature to match the projection of the states shapefile. Finally I assembled all of the data frames on one map and organized them as seen in Figure 1 below.
Figure 1: Maps and their projections The final portion of this project required me to resolve projection problems between two features being projected on the same map. The first was a shapefile I added of Central Wisconsin counties. This shapefile had an undefined geographic coordinate system. This meant that I needed to choose a geographic coordinate system for this shapefile. Based on the information from the metadata that was provided to me in the lab 1 instructions, the geographic coordinate system I gave this shapefile was North America 1983, or NAD 1983. To do this, I opened ArcToolbox, and under the Data Management Tools I selected Projections and Transformations and then Define Projection. I selected the counties shapefile and the geographic coordinate system I wanted and clicked OK to define the projection.
Figure 2: Map of Central Wisconsin Counties and Rivers The next step was to add the rivers polyline feature from my lab data. This shapefile brought up another issue because the projection of this shapefile was not the same as the projection of the counties shapefile. Both projections need to be the same in order for the map to be displayed accurately. To solve this problem I went back to ArcToolbox and instead of choosing the Define Projection tool I chose the Project tool. I input each feature separately into the tool and selected the desired output, this being a North American 1983 StatePlane projection of Central Wisconsin. Clicking OK created a two new features to replace the old features on the map. I removed the old counties shapefile and the old rivers polyline and I was left with an accurate map of Central Wisconsin counties and the rivers that run through them.
- The results of the maps (Figures 1 and 2) and my methods reflect my understanding and ability to resolve issues related to geographic and projected coordinate systems.
- Michigan Department of Transportation. (2016). Retrieved from michigan.gov/mdot.
- Maribeth Price. (2016). Retrieved from Mastering ArcGIS and mgisdata.
