The recorded location of an observation of an Element may vary from its true location due to many factors, including the level of expertise of the data collector, differences in survey techniques and equipment used, and the amount and type of information obtained. This inaccuracy is characterized as locational uncertainty, and is assessed for Source Feature(s) based on the uncertainty associated with the underlying information on the location of the observation.
Four categories of locational uncertainty have been identified, as follows:
Negligible uncertainty is less than or equal to half the minimum mapping unit (mmu) in any dimension. Source Features with negligible uncertainty are based on a comprehensive field survey with high quality mapping and a high degree of certainty. For example, on a 1:18,056 scale map with an mmu of 9 meters (diameter), a Source Feature will have negligible uncertainty if the uncertainty is less than 4.5 meters in any dimension.
Linear uncertainty is greater than half the minimum mapping unit (mmu), and varies along an axis (e.g., a path, stream, ridgeline). The true location of an observation with linear uncertainty may be visualized as effectively sliding along a line that delineates the uncertainty.
Delimited uncertainty is greater than half the minimum mapping unit (mmu), and varies in more than one dimension. The true location of an observation can be visualized as floating within an area with a boundary that can be specifically delimited. Boundaries can be defined using roads, bodies of water, etc.
Estimated uncertainty is greater than half the minimum mapping unit (mmu), and varies in more than one dimension. However, a boundary cannot be specifically delimited based on the observation information, i.e., the actual extent is unknown. The true location of the observation can be visualized as floating within an area for which boundaries cannot be specifically delimited. Source Features with areal estimated uncertainty require that the user specify an Locational Uncertainty Distance to be used for buffering the feature to incorporate the locational uncertainty.