Navigation Part I - Preparation

Introduction

A huge part of geography is based in the old school techniques of navigation. In the past, the research for improvement in the navigation methods was the main reason for the development of geographic knowledge and exploration. Nowadays, for navigation, the technology of GPS is predominant for almost all the purposes. However, how it was already mentioned in earlier reports, it's essential to have the knowledge of the alternative ways, so you don't fully depend on this kind of technology, since it can fail on you.

Accordingly, this exercise consists in navigating at the priory using different methods: at first, a navigation map and a compass; in following week with a GPS, but no map; and for last, in the last week, with the GPS and a map. The goal is to find the advantages and disadvantages of the tools used and which ones are essential. However, before any of those navigations be done, it’s necessary to get prepared for it. Then, in this report the main elements to be prepared to go on the field will be explored, by elaborating the necessary material.

Methodology

For the first week of navigation, with compass and a navigation map, it’s necessary first to produce the actual navigation map with the elements necessary, and since there won’t be any device to calculate the distance, the measurement of the personal size of each step is made.

The method to find the actual size of each step is by creating a known distance line – in this case of 100 meters – and walk by it for multiple times counting steps, until it doesn't have reasonable discrepancy.  To measure how much was 100 meters, the laser device was used: one student (Amy) was targeting and another student (Me) was moving and being targeted until it reached the necessary distance. (Figure 1) Once reached, the spots were marked with snow, so the students would know where to start and finish. After having the result of the number of steps, a simple calculation will result in the size of the step, which in this case was 1.45 meters per step.

Figure 1 - Right: Amy using the laser device to target the distance of 100m. The snow on the floor worked as the start point for the pace count. Left: The path of 100 meters while I was being targeted by the laser to guarantee a precise measurement.

In the production of the map, the location where the navigation will be made had to be analyzed. Different elements can work as a reference depending on the place you are. If it’s an urban area, maybe building and streets are important reference features. However, the priory is located in an open field, with basically only vegetation around and very few buildings. Thus, the reference in this case has to be the natural features, as vegetation types and elevation.

After identifying the important elements for the map, the related data have to be gathered together. For that, it’s important to evaluate the different sources one can access data. For convenience, the main data was available for the whole class. However, to find data related to elevation and vegetation, a good source would be the USGS, within The National Map Viewer. For this map the Digital Elevation Model was obtained from USGS, however, the two feet contours for elevation were obtained by UWEC survey, at the time the university bought the area. The imagery was obtained by the Wisconsin Regional Orthophotography Consortium 2010 (WROC 2010).

With the data gathered in ArcMap, the challenge is to insert the most of useful information as well as not making the map very polluted and busy. For that, some cartography techniques like transparency and change of colors were used to maintain most of information, but emphasizing only the ones that were essential. Since the work was being done as a group, each one started its own map (Figure 2), but after seeing the progress of each, the whole group focused in one of the maps, giving suggestions and improvements.

Figure 2 - Individual Map

The purpose of the map is the main element that has to be remembered while working with different priorities in the cartography. Since the objective was for navigation in a certain portion of the map (Area of Interest in the Figure 2), the main references were prioritized, while areas outside this area could have other map elements like north arrow, scale and others.


Discussion

In this project was possible to experience how troubleshooting enforces knowledge of a given subject, in this case, projections. One of the most important features – the 2 feet line contour – didn’t have the projection information. In Arc Map, by adding this data to your session, the on-the-fly projection will automatically put the feature in the data frame projection. However, it will just work if the data frame projection is the same as the one the feature was created. Otherwise, the coordinates won’t make sense and the feature will be placed far off.

With this kind of issue, it’s also common to make confusion with two different tools inside Arc Toolbox: Define Projection and Project. The first will simply label the feature with a projection, overwriting the last one, but it won’t change its coordinates. The second changes the coordinates, using complex math, creating a new feature, projected. In this case, one could think that it was necessary to run the project tool, but that wouldn’t be possible since the feature is not even labeled yet.

Thus, it was necessary to analyze the extent of the data, going to its properties, in the source tab. There, you would have the extent numbers, however, without its units (Figure 3). By looking at that, it’s easy to detect if it’s a projected or geographic coordinate system because of the units – big numbers for projected (meters or feet) and small numbers with a lot of decimals for geographic (degrees).

Figure 3 - When dealing with a undefined coordinate system, it's possible to interpret the extent coordinates and try to find the correct projection.

Then, it was known that it was a projected coordinate system, and because of the purpose of the map, that this feature was located in Eau Claire. Considering the main coordinate systems, there were some options: UTM, Wisconsin State System and Wisconsin State Plane System – Central. The first thought was about UTM, but in this system, the Y coordinate in the north hemisphere means the actual distance of the place from the equator. Y coordinates about 476 kilometers didn’t seem right for an Eau Claire location. 


Since the feature has an undefined coordinate system, it’s not a problem to overwrite the label over and over to make tests using the Define Projection tool. Then it would be fine to test the UTM coordinate system, even though it seemed odd. However, the data format was DWG, so the Define Projection tool couldn’t simply be used on Arc Toolbox. It was necessary to go on Arc Catalog and define the projection for the entire dataset. Once done, the results showed that UTM was really not the right projection.

Figure 4 - In the same coordinate system, there's multiple variations of units and datums.

By looking again to the extent, it sounded reasonable for the Wisconsin State System. However, there’s a big list of Wisconsin State Systems, depending on the datum or units (Figure 4). As mentioned before, there’s no problem in testing different projections, so the first test was made with “NAD 1927 Wisconsin TM (Meters)”. Finally the feature was placed at least closer than Eau Claire, however, it was still too far off the Area of Interest. Even if a reference as the Area of Interest was not available, it would be possible to perceive the misplacement of this feature by interpreting the contour lines along the landscape in the satellite image: they don’t fit at all. (Figure 5)

Figure 5 - The feature was placed far to north-east from the Area of Interest. Plus, in the zoom of the contour lines, it's possible to notice how they didn't fit with the landscape of the satellite image.

That’s where the knowledge not only about coordinate systems and projections, but also about datums are useful. Different datums (NAD 1927, NAD 1983, WGS84) don’t match each other, even if you have the same projection and coordinate system. Hence, even setting up everything in the right properties (coordinate system, projection and units) won’t help if the wrong datum is chosen: the features will be far off, as it happened in this project. The right datum in this case was NAD 1983, which was discovered in the next test: the feature fit the landscape and fell inside the Area of Interest.

Furthermore, after dealing with the data issues, it was interesting and challenging to deal with a considerable high amount of information in the map, without making it cluttered and busy. The contour lines could easily be less emphasized by adding some transparency to it, or changing its color to a lighter gray.

For the grid, it was a little more complicated than that. The goal would be to plot point on it, so the finer the interval, the more precise the plotting would be. However, the lines of a small interval could almost inhibit the readability of the actual features in the map. Some intervals were firstly tested and the decision of keeping with a 20 meter interval came after editing it in a way it would lose emphasis in the map. That way, the lines were changed from continuous lines to dotted lines. To avoid confusion with the contour line, the color was changed.

Conclusion

This exercise exposed two faces of map-making: the strict rules of data sources and the flexibility of cartography. It was important to reinforce the dynamic of geography and how everything needs to be thought in its different purpose and background.

When dealing with coordinate systems, projections, datums and units; you have to be very exact and certain of the information to keep data reliability and accuracy. Technology can often support this task not to be so exhaustive, as seen by the use of on-the-fly projection, what usually works to match two different features in the same place, even though one might not have a defined projection. However, this exercise was an example where this tactic didn’t work. Thus, when obtaining data, it’s crucial that you always have the necessary information to deal with it. Unfortunately, it’s not common to find all the necessary details in the metadata, so it’s essential to keep track of the data sources and always get the necessary information about it.

However, a more flexible task was also experienced by using the cartography to manage the map-making. In this area of geography, there’s no such rigorous since there’s no right and wrongs, but a number of possibilities that can meet your goals of presenting data. It doesn’t  mean that anything that is done will be correct, it’s always fundamental to focus on the purpose of the map and test different forms of dealing with different priorities. That can be challenging, exactly because there’s not only one right answer and it’s commonly a trade-off.

Summarizing, the results of the exercise were satisfactory, but mainly, dealing with these challenges was a great experience to improve and reinforce our geographic knowledge.