Mapping Proposed Acquisitions
This section describes how to use GIS to clearly describe proposed acquisitions.
The most common tasks land trusts have is to secure land through purchase outright or of a conservation easement. Once your land trust has used GIS to generate basic site maps, you might consider more advanced approaches to acquisition mapping:
Most project maps generally depict similar information - topography, property boundaries, roads, water, elevation, etc. However, the quality of property acquisition maps can be raised greatly (along with their effectiveness with trustees, donors, stakeholders, etc.) by applying the following:
- A well designed frame for the map itself
- Shading the elevation and overlaying that with slightly transparent polygons depicting key properties
- A high resolution aerial photograph
One of the most useful analyses is to evaluate what can be seen from the property and what others can see on the property. The tool for doing this in GIS is called viewshed analysis. Using a specialized tool or extension (e.g., in ESRI ArcGIS you will need the Spatial Analyst extension), you define viewing points on a base map of elevation data. You set the height off the ground and distance of view, and the software will calcuate all of the areas around you that can be seen from that point.
More advanced viewshed analyses define multiple viewing points (ten points in our community that represent places from which most people will view our property), and can even weight those points to create a probability or cost surface, instead of just a plain viewshed. Or, you can define a drive line along one or more roads and then calcluate all of the viewscapes that you can see in that drive.
Viewsheds generally don't take into account vegetation or buildings, so while an area "can" be seen from a point, it may or may not actually be able to be seen.
Habitat: Habitat maps are generally based on vegetation data. Key plant species are mapped directly; for wildlife, vegetation data supports inferences and models that are created to show plant and animal relationships. This information can greatly enhance how you describe and understand a proposed property. A good source of information on this subject is the Natureserve web site data section
A key factor in many public agency funding decisions is the presence of endangered habitat. By using data that portrays the general locations (or for private use, the specific locations) of federally (or state) threatened and endangered species, better information can be conveyed about the property's importance.
More information on this data can be found at the U.S. Department of Fish and Wildlife web site, including their TESS
subsite which has searchable data on endangered species.
In many cases, such data can only be displayed as general locations, to prevent inappropriate use of this information.
Other Maps: Soils, geology, land use and other information can be used where appropriate. See the GIS Data section
of this web site for more information.