Base map data –planimetric features (roads, buildings, utilities, etc.), orthophotography, and elevation (contours, spot elevations and, increasingly, LiDAR collected 3-D surfaces) – is the foundation of municipal GIS. Municipalities that rely on their GIS programs generally update their base map data sets every few years.
In this post, I describe five planning steps you can take to reduce costs and define a base mapping project that is appropriate to your needs and budget.
STEP ONE: Evaluate Current Data
The first step is to review your existing base map data holdings to determine how much base map updating you need. Here are three things to consider:
- Consider the type and pace of change in your municipality – If there has been little physical change in infrastructure in your municipality, perhaps a new orthophoto layer would suffice for some of the update cycles, rather than a full planimetric mapping effort
- Check to see whether data sets like utility features have been accurately surveyed on the ground so that they might not need to be photointerpreted as part of a base mapping project.
- Determine the accuracy you need for departmental functions and whether the accuracy of current features matches the use, for example, do you need greater horizontal accuracy to support utility management and planning than your base map data currently provides? Are there flooding issues or development projects that require greater vertical accuracy?
Limiting the base mapping project to orthophotography updates or reducing the collection and mapping of features translates into lower costs. On the other hand, if current mapping does not support critical government functions, an investment in higher resolution base mapping can and should be justified by those beneficial uses.
STEP TWO: Identify Outside Resources
The second step is to inventory other data resources so that you do not needlessly (recreate) data that already exists and may be “good enough” for your purposes, or duplicate the effort of other data collection programs:
- Research what is already available for your area. Many states and counties have base map programs with freely available data that could meet your needs. Usually these are of a smaller scale (lower accuracy) than what you may desire, with the pixel size being between 1foot and 1 meter. Most often orthophotography is available. I expect more elevation data to become available from large area LiDAR programs. Detailed planimetrics are less likely to be availableexcept for major features such as roads. That said, each state has a website listing many available GIS data sets.
- Some states and regions have programs allowing municipalities or groups of municipalities to buyup for higher resolution imagery and other base map data products in conjunction with a planned statewide program.
STEP THREE: Team Up
Seek out opportunities to team up with adjacent entities to reduce costs. Planning amd mobilizing for the flight, ground control and production incurs a significant portion of a project. If these costs can be spread over a larger area, the unit cost will be lessened. It can be tricky to coordinate with other jurisdictions and it can lengthen the lead time for base map acquisition, but it’s worth looking into.
STEP FOUR: Set a Budget
Now that you’ve defined your base mapping project and scope, it is time to develop a realistic budget: Talk to vendors and get a realistic cost estimate for what you want to do. Get advice on vendors from other GIS programs and ask for “back of the envelope” quotes from several of them. Ask for some options in scale or content to give you a sense of the range. Be sure you have money in place for the project. With an April flight, it is possible for the project to span 2 fiscal years- flight and ground control pre-July 1 and the production in the new fiscal year after July 1.
STEP FIVE: Plan for Acquisition
A detailed RFP ensures you get comparable, competitive pricing for the specification and size of project you have defined. It should include detailed specifications on scale, map projection; flight conditions; imagery; ground control; accuracy; detailed planimetric database design; and specifics of the deliverables.
The four main tasks in base map procurement are: (1) Planning; (2) RFP management and vendor selection; (3) Quality review and acceptance; and (4) Project management. In an upcoming post, I’ll talk more about RFP management and vendor selection.
By David Weaver, GISP, Vice President, Head of Cartography, who has helped clients to plan and complete more that 60 large-scale base mapping projects.
In performing all of these steps you have a choice whether to tackle these tasks yourself or ask for outside help. In my experience, a little outside assistance can save you time and money. Contact me to discuss your project.