Location, Trigonometry, and Measurement of the Sphere - Spatial Mathematics: Theory and Practice through Mapping - page 46

In the following activity section, you will have the opportunity to use dif-
ferent coordinate systems, such as latitude and longitude, the Military Grid
Reference System, and the Public Land Survey System.
2.6 Practice: Coordinates using different systems
Access the National Map Viewer from the USGS ( http://viewer.nationalmap.gov/
viewer ). Click on the Find Coordinates tool and click on St Louis. What are the
coordinates of St. Louis in Decimal Degree Latitude-Longitude (DD), in Degrees
Minutes Seconds Latitude-Longitude (DMS), and in the Military Grid Reference
System (MGRS)? These readings are, depending on where in the city you are
clicking, 38.62484 degrees north, 90.20135 degrees west in DD, and 38 degrees
37 minutes 29.427 seconds north, 90 degrees 12 minutes 4.877 seconds west in
DMS. It is 15SYC4363578862 in MGRS. Calculate the DM coordinates yourself
using the values you just discovered using the National Map Viewer. The DM
coordinates are calculated as follows: 29.427/60 = .49045, and therefore the
latitude of St. Louis in DM is 38 degrees and 37.49045 minutes north. The
longitude is 4.877/60 or .081283, so the DM longitude of St. Louis is 90 degrees
12.081283 minutes west. What are the coordinates of your own community
according to each of these four systems?
Find coordinates using several different methods by using GPS Visualizer ( http://
www.gpsvisualizer.com/calculators ). This tool allows coordinates to be calculated
and mapped in several different systems, as well as distances between two points
on the globe.
Use the Find Latitude and Longitude ( (http://www.findlatitudeandlongitude.com/), ),
and search for other latitude and longitude tools. How do these tools compare?
Which tools give insight into the algorithms used? If they do not give information
about the algorithms used, can you trust them? Keep in mind one of our central
themes of this topic: Know your data, and know the underlying methods and
assumptions that led to the creation of the data in the first place. Web-based
tools are rich and varied, but need to be carefully scrutinized.
Examine the Principal Meridians and Baselines map at the Bureau of Land
Management on http://www.blm.gov/wo/st/en/prog/more/cadastralsurvey/
meridians.html . This map shows the meridians and baselines that make up
specific zones in the Public Land Survey System (PLSS) in specific states. What
principal meridian and baseline covers most of the land of Wyoming, Colorado,
Kansas, and Nebraska? This is the Sixth Principal Meridian and Baseline. How
many zones cover the state of California? The map shows three of them: The
Mount Diablo, covering about 2/3 of the state, the Humboldt covering the
northwest corner, and the San Bernardino, covering the southern third.