Field Navigation Part One

Introduction
This weeks assignment consisted of preparation for a field navigation exercise that will take place at the Priory.  This land, purchased by the university to be a day care facility, is located to the south of the city of Eau Claire.  The image below shows that the land that we will be navigating through is mostly wooded.

Image 1. Area of Interest

 

The activity will consist of a series of points that we will need to navigate to using a compass and maps that we created.  We will not be using a GPS, as the purpose of the exercise is to learn to navigate without the aid of technology.  Since this area is mostly wooded, a GPS might not be very accurate anyways.

Methodology
The first step in our preparations involved establishing every person's pace count, which is the number of steps taken in a given distance.  This will be useful for our navigation because we will not have a GPS available, and we can use our pace count to tell how long of a distance we are walking.  A laser rangefinder was used to find a distance of 100 meters in a parking lot, and the end points were marked with snow.  Each person in the class then walked the distance, keeping track of the number of normal paces that they took.  After walking the distance three times, I found my pace count to be 65.  It should be noted that this was done on a sidewalk, and that a pace count might differ when walking through the woods and avoiding obstacles.

After the pace counts were established, our next task was to create the maps that we would use in our navigation exercise.  There was a suite of data sets available, but it was up to us to determine what would be useful to have on a our maps.  The data available consisted of: a topographic map of the region, color and black and white orthoimages, two foot contour intervals, five meter contour intervals, shapefiles of the area of interest, and a DEM.

When working in GIS, it is extremely important to be aware of coordinate systems.  ArcMap uses on the fly projections to project data that are in different coordinate systems.  This is nice for displaying data as you are using it, but any analysis should be done with data in the same coordinate system.  It should be noted that it is best practice to work with files in the same coordinate system to prevent errors and inaccuracies.  There are many different coordinate systems, and the appropriate one should be chosen to work best with the area of interest.  The area of interest for this project is very small, so a state plane or UTM coordinate system is ideal.  The UTM 15 North coordinate system was selected.  This coordinate system will work well because we can create a UTM grid and overlay that on top of our maps to aid in the navigation.

During the beginning of map construction, the two foot contour data was giving us problems.  This file was converted from a CAD data set, and did not have a projection.  When it was added to the other layers in ArcMap, it was not displayed.  To solve this problem, a blank document was opened, and the two foot contours were the first file added.  After this, the other data layers were added in the UTM 15 North projection.  I decided to make two maps for this navigation exercise.  The first consisted of the DEM, two foot contours, and a UTM grid.  The DEM covered a much larger spatial extent than our area of interest, so the Extract by Mask tool was used to extract the area of interest from the final file.  This smaller area had a smaller range of values, which made for better symbolization.

Map 1. Navigation Map with DEM and Two Foot Contours

The second map was to have a much more simple design.  For this, the orthophoto was used as the base, and the area of interest and five meter contours were overlaid.

Map 2. Navigation Map with Orthophoto and Five Meter Contours

    Each person in our three person group created their own maps, and then as a group we were to collaborate and choose two maps that we liked best for our navigation.  My second map of the orthophoto and five meter contours was chosen, as well as Hannah Bristol's map pictured here.

Map 3.  Hannah's Navigation Map

Discussion
This weeks assignment was based on preparations, and a more detailed account of the exercise will come next week after we actually partake in the activity.  The preparatory work did have value in terms of establishing a pace count and discussing how it can be used for navigation, as well as stressing the importance of knowing and understanding coordinate systems.  When working with different data sets, they should always be in the same coordinate system.  If not, the project tool should be used to convert them.  Also, the appropriate coordinate system should be used, depending on the extent of the area of interest.  For a small region like this, the UTM Zone 15 North works very well.  A state plane coordinate system could also be used, but one must be aware of the extent of the zones, because you do not want the area of interest to overlap into two or more zones.  Finally, map elements were an important aspect of this exercise.  We were to determine which files we wanted to have on our maps without them being too cluttered.  Scales, north arrows, grids, and the sources of data also had to be included.