Maps GPS GIS

Today you are going to become familiar with handling spatial data, both in paper and digital forms, something you will do throughout this class. You will learn how to read topographic maps to determine your position and corresponding location in another map or device. You will also learn the particulars of organizing spatial data, such as a datum, grid system, and projection. You will learn more about the Global Positioning System (GPS) as well as some about manipulating spatial data using a Geographic Information System (GIS).

Your goal today is to compare GPS data for 7 locations (Stations) that you acquire, with precise location data for these sites. You will be acquiring GPS data with your phones. In addition I have already acquired highly precise ~50 cm GPS data for the same Stations which you will make use of later.

Field Acquisition
You will work in groups of 2 in the field, with each student making measurements with their phones.

Enclosed is a map of the Stations, shown in yellow and labeled 1 to 7, plotted on a 7 ½ min quad top base map. Note the date of this map is 1978 so a lot has changed on campus since it was published. Use of this map is intentional. It is good for you to get used to using different vintages and scale of maps, as well as going between different digital devices and different quality paper maps. Note also that the grid system shown is UTM, which is different from what your phone uses (Lat Lon). Again, intentional, but also note that because it is UTM, the units are in meters and thus very convenient. Determine the fractional scale of the map to see what I mean.

Your job is to find these Stations in the real world and survey in their Lat Lon location using the Google Maps or Apple Map app on your phone. Make sure location services is on so that GPS works. The workflow is to read the topo map and compare it to what you see in the map app (turn satellite or topo as a base in the app). Once you know generally where a station is, walk over towards that location, and look for a piece of paper that shows a square with a circle and cross inside indicating a W&L Geology Lab Exercise location (commonly called a ground control point or GCP). If you see goodies at a station, feel free to partake.

Each member of your group should use their phone and survey in the Lat Lon location by dropping a pin (hold finger down) right on top of the survey location. Depending on the app and version you may see the Lat Lon values at the top of the page or have to scroll down, or click share before you can see the values of Lat and Lon. Being scientific we want to isolate the variables so let’s wait at least 30 sec. and for the blue dot to stabilize before you collect a point. If your location shows uncertainty (blue transparent sphere in Google Maps or if you notice your blue dot still jumps around, or is not really in the spot you know are), then you should wait until it stabilizes before collecting the point. Not waiting long enough for the GPS reciever to get a good lock on your position is by far the biggest data-collection issue to be aware of.  Make sure that the location seems to be where you think you are and that it is not moving.  If that takes longer than 30 sec. then so be it.  Likewise we want to be as accurate as we can, so write down all significant figures. Interestingly the number of digits to the right of the decimal point will matter in this case. Write these down on the recording sheet provided (one for each surveyor).

Figure out where the next Station is and find the next ground control point and repeat the above acquisition. So you will have a total of 7 points per surveyor from the phone. Once you have completed the acquisition you can take a break, and we will reconvene in the classroom Rm 218 at around 3:00 PM (or about 1 hr after we start the field acquistion).

Computer Lab Work
Enter all of your data into the Google Sheets through the link that I email you. We will have a total of 22 points for each station, and one Google sheet for each station. Double check your entries by requiring your partner to inspect what you input for each station.  Data-error entries just screw up the data to be analyzed later. It is important to have your data entered into the sheet as soon as you can because everyone will be relying on each other's data.

Do NOT make any of the calculations (discussed below) in this Google Sheets document. Download the file to your computer and make your calculations there. The reason is that I want all students/groups to figure out how to do the calculations themselves.

Next you will load all of the data into a GIS called Global Mapper. Depending on the time allowed you may finish this in class, but likely you may have to do it outside of class. Work in your groups at first for this, so one member of your team log onto a Geo Lab computer and then follow the directions below. Ultimately I want everyone to be able to do this, so at the end of the class each of you copy of your GlobalMapper project to your own Box Drive.

The Global Mapper program is available on the Geology Dept. computer lab machines as well as the IQ Center lab machines (in the back room).  The advantage of these is that they all have 2 monitors and are very fast.  You would be surprised how important it is to have a big screen when working with maps on a computer. 

The data that you are going to load below is located at R:\courses\GEOL_101-02_Winter_2023.  This is a server that is accessible to you as a geology student on the Geo. lab and IQ Center lab machines.

Briefly the steps are listed below. I am here to help you with them.
1) Open Global Mapper.
2) Load the DRG topo map of Lexington.
3) Change the datum to WGS84.
4) Load the Differential GPS points I surveyed.
5) Export from Google sheets all seven phone-surveyed station sheets as .csv files.
6) Import each sheet into Global Mapper.
7) Display the data in a way that allows you to see a difference between the phone-surveyed and Differential GPS points. Do this by making the Differential data Yellow Dots size 2, and show the label information. Then make the class surveyed points from your phones Blue Dots size 2.
8) In Excel calculate the Mean and Median of each of the 7 Stations. Export as CVS files and then import into Global Mapper. Make the phone mean a Red Dot size 2, and the phone median a Green Dot size 2.
9) Load the NAIP air photo and look at how the points sit relative to features in the air photos.
10) Make a printable map with a proper scale, grid lines, etc. You do this by using the Map Layout Editor.

A detailed description of doing the above steps in Global Mapper.

Deliverables
In class you will have been working with others, but you will turn in your own report. So make sure to have copied the Global Mapper project for your group and after the end of class you need to work with it yourself (so that you can learn how to use it).

Due Fri. Jan 13:
Two maps. One map should have a base map of the topo (DRG) map. The other with a base map of the air photo. Both should show the points, with a UTM grid, info on the projection and datum, a graphical scale, and legend. If you want to make a zoomed in one to show more detail, feel free to do so, but you need at least the first two, as described in the detailed directions above.

You do not need to have a formal style for the report.  It just need be a paragraph or two summarizing the accuracy of the data the class collected relative to the Differential GPS and features in the air photos as a pdf. Try and quantify this in some way (hint there is a ruler tool in Global Mapper). Which is a better indicator of the class phone measurements, the mean or the median? Why is that the case? Make sure to discuss if all 7 stations appear to have the same accuracy relative to the Differential GPS. If they do not, speculate on why that may be so. Finally discuss how we could potentially improve the accuracy of the phone data.

Note, your grade is based on both the maps you produce (with all of the ornamentation listed above), and by how much you address the above questions.

Print all this out, with your names on all sheets, and bring to class on Friday the 13h!