Free GIS Data on the Web: Not All Data Is Created Equal!June 15, 2014 Wind Energy
Most land and energy development projects, regardless of size or scope, will require some basic geographic background data before design begins. Traditionally, that information is gathered with a ground-based survey or a custom aerial mapping flight. In recent years, there has been a flood of free geographic (GIS) data readily available on the internet, including high-quality topography and aerial photography covering many parts of the country. Though, there are situations in which this free GIS data will work just fine on a project, taking the time to understand what you are using will lend confidence to the decision and could prevent lost time and costly errors down the line.
Determine the density and quality of the data obtainable.
If high-quality elevation data, such as LiDAR, isn’t available online for your project area, you might feel stuck using older, low-quality topographic data sets. While this might be fine for concept- or preliminary-level design, it likely won’t be sufficient for final construction documents.
Today’s high-tech, GPS-controlled, construction equipment requires that the engineer’s design model be equally as precise. If low-quality elevation data is used during design, this requirement will not be met, rendering the final product unusable by the equipment’s technology. Even if publicly available LiDAR does exist, the quality should be vetted to make sure it will meet the project’s needs - especially if there will be detailed grading.
You found some high-quality data. Is it obsolete?
There is the issue of the timeliness of GIS data on the web. A three-year old aerial photo with LiDAR data might work well as the basis for a preliminary design. However, it is considered too old to be used in the preparation of an ALTA survey. The ground may have been graded or altered since the public LiDAR flight, making the data obsolete. It is always good practice to check the flight dates of the data before using it on a project.
There is no one fast rule for using free online geographic data on a project, but fortunately many opportunities exist that make it acceptable, particularly during the early phases. It simply takes a bit of due diligence to ensure that what you are using fits the project need long term. Online data can save a project significant time and money if properly used. Other times, projects will benefit most from a custom aerial mapping flight or ground survey. The additional investment in the project will pay off come construction time. Keeping in mind the underlying need and desired outcome is critical in making the best choice for obtaining project data.