Using Earthmate Blue Logger GPS and DeLorme Mapping Software to Create an Accurate Digital Map of a Parcel Part I Creating a Map of the Parcel Boundaries Written by Mark Genaris Overview This spring I inherited a 50-acre parcel of land from my uncle. My first order of business was to collect some basic geographic and resource information about the property to determine how I would use it over the next few years. For example, I would like to build my own home somewhere on the property, but I don t know where I can do that yet. I would also like to put in a garden, identify possible timber lots, and leave some areas undisturbed for wildlife habitat and passive recreational uses. I ve seen the land a couple of times on foot but, to really gain an overall perspective, I wanted to create an accurate digital map of the property s features and overlay them on an aerial photograph. Rather than rely on outdated maps, I wanted to create the map using real world data. To accomplish these tasks, I thought I would try to use Global Positioning System (GPS) and Geographic Information System (GIS) technologies. I asked around for advice on powerful, and yet affordable products, and soon found the consensus to be that for the price, DeLorme s XMap/GIS Editor software and Earthmate Blue Logger GPS receiver are the way to go. The first thing I wanted to do was to map the property boundaries so that I could see where the property is in relation to the surrounding land. This step was especially important for locating the best areas on the parcel to preserve as wildlife habitat. I wanted to establish these areas next to existing conservation land that may be adjacent to my property. I also wanted to see the property lines on an aerial photograph to establish a search area for future mapping efforts. Seeing the boundaries on the aerial photograph will help me to focus my attention on the areas where I am trying to identify and locate certain features, such as wetlands and tree species. Assigning Logging Preferences After removing the packaging and marveling at the small size and simplicity of the Blue Logger GPS receiver, the first step was to charge the receiver and then connect it to the computer via its built-in Bluetooth wireless connection. The Bluetooth connection eliminated the hassle of wires and made it simple to configure the device. Using Blue Logger Manager (the software that comes with the receiver), I configured the receiver to collect GPS points every two seconds, and to collect points as standard data. The standard data setting (as opposed to raw data) is primarily designed for situations where you are moving with the GPS unit while collecting data. Setting the device to collect points as raw data is more suited for when the GPS unit remains stationary. The benefit of collecting points as raw data is the ability to post process the GPS files after returning from the field for improved accuracy. 2004 Earthmate.com Page 1
Figure 1: Connecting Blue Logger to the computer. Figure 2: Configuring the Blue Logger. Collecting and Downloading GPS Data After configuring the Blue Logger, I was ready to do the actual GPS data collection on the property, which was as simple as turning on the receiver, waiting for the GPS light to flash green (which indicates a 3-D satellite connection), and walking along the parcel boundaries. After collecting the data, I returned back home, connected the Blue Logger device to my desktop computer using the wireless Bluetooth connection, and downloaded the GPS files. Figure 3: Downloading GPS data to the computer. 2004 Earthmate.com Page 2
Downloading Aerial Imagery Using NetLink Since I wanted to overlay the boundary lines on an aerial photograph, the first thing I did before looking at the GPS data was to download an Aerial Data Pack (ADP) of the property using XMap s NetLink feature. ADPs are customized datasets containing USGS Digital Ortho Quads (DOQQ), USGS 7.5 Minute TopoQuads, USGS Digital Elevations, and DeLorme Sat 10 satellite imagery. The integrated NetLink function made it easy to collect the image files I needed, without having to hunt around for hours on the Internet. A grid popped up on the screen, I selected the grids that contained my site, and then downloaded the data. The aerial photograph (DOQQ) automatically displayed on the screen. Note: You can also use NetLink to download aerial imagery in Topo USA 5.0. Figure 4: Selecting ADPs from the NetLink Tab. Figure 5: View of a DOQQ on DeLorme s XMap interface. 2004 Earthmate.com Page 3
Importing the GPS Data into DeLorme Software To see the parcel boundaries overlaid on the aerial photograph, I imported the downloaded GPS files into XMap/GIS Editor using the Draw function, which displays the GPS data as a line. When viewing the lines on the screen, I noticed there were a few locations that had some unusual spikes and turns, which were caused by sporadic interferences with the satellite reception. There are many things that block and reflect satellite signals on their way to the GPS receiver, including trees (many on my parcel), buildings, cars, fences, and even people. However, XMap s Draw function made it easy to edit these spikes and turns to smooth out the line. Note: Most DeLorme mapping programs are equipped with Draw functionality. Figure 6: Boundary line before editing. In this example, the parcel boundary followed a steam underneath dense fir trees. Figure 7: Boundary line after editing. 2004 Earthmate.com Page 4
Conclusion Mapping the boundaries of my 50-acre parcel from real world GPS data was a crucial first step in achieving my goal of creating an accurate, up-to-date digital map of the property. I can now use the parcel boundary map as a base map onto which I will overlay additional data, including the locations of wetlands, tree species, soil types, and wildlife habitats. I can also display which areas to leave undisturbed, which areas to harvest timber from, and the best locations to build a house or put in a garden. Being able to see the GPS data I collected on the screen, enabled me to make decisions that otherwise would have been difficult to make. Best of all, DeLorme s products enabled me to do all of the work by myself, eliminating the need to hire expensive contractors. In Part II of this article, I will talk about how I used Blue Logger GPS and XMap/GIS Editor to improve the accuracy of the aerial photograph (DOQQ) I downloaded from NetLink, and how I completed my digital map of the property. 2004 Earthmate.com Page 5