The "Radius From Address" and "Drive Time" region selection options allow the user to select a point on a map and all regions within a certain drive time or radius of that point.
Since Lightcast data is only available in terms of pre-defined geographies (ZIPs, counties, etc.), the input drive time or radius must be translated into these geographies. Choosing the smallest available geography that is compatible with the type of data selected is best practice--it allows for the tightest possible region definition.Another decision the user must make is what to do with regions that intersect the desired drive time or radius. Inevitably, some ZIPs (or counties or tracts or states) will fall partially inside and partially outside the drive time or radius. The "Include regions" dropdown allows the user to decide how these regions should be treated:
Contains region's centroid: Include all regions whose center point falls inside the defined drive time or radius. This is the center-of-the-road inclusion option--a lot of the region in question must fall within the defined radius or drive time to be included.
Contains entire region: Include only regions which fall entirely inside the defined drive time or radius (alternatively, if a region sticks out of the radius or drive time, do not include it). This is the least aggressive inclusion option, and will include the fewest regions.
Contains part of region: Include any region which falls even partially inside the defined radius or drive time. This is the most aggressive inclusion option, and will include the most regions.
We calculate our "centroid" in one of two ways: aggregated or disaggregated. When a user selects multiple MSAs (Metropolitan Statistical Areas) in an aggregated manner, the system finds the center of the combined regions. If a single MSA is selected, the system returns the centroid for that specific region. Our maps are based on the WGS84 reference system, utilizing latitude and longitude coordinates.