Datum
Definition
A Datum in GIS is a reference model of the Earth’s shape used to define geographic coordinates. It determines the position of latitude and longitude lines, and provides a framework for referencing locations. There are horizontal datums (like WGS 84, NAD83) for map accuracy and vertical datums (like NAVD88) for elevation reference. Different datums are based on different ellipsoids and base measurements. Using the wrong datum can result in misaligned data or spatial inaccuracies in analysis.
Application
GPS devices use WGS 84 as the default datum. Surveyors may use local datums for more precision. GIS analysts must check the datum when importing data from different sources to ensure alignment. Datum transformation tools allow conversion between systems when necessary. Accurate datum use is critical in applications like flood modeling, construction planning, or aligning infrastructure across boundaries.
FAQ
1. Why is a datum important in GIS?
It defines the Earth's model used for locating features; incorrect datums cause alignment errors.
2. Why is a datum important in GIS?
WGS 84 is a global datum used by GPS; NAD83 is a North American datum aligned more closely with that continent’s surface.
3. Why is a datum important in GIS?
They may appear misaligned unless transformed to a common reference system.
4. Why is a datum important in GIS?
Using GIS tools that apply transformation equations and parameters to align coordinate systems.