Abstract: A facility for representing a set of items each potentially having a value for each of a group of attributes is described. The items are represented in a database made up of two or more discrete components. Each component corresponds to a proper subset of group of attributes, and represents for every item of the set the values of its proper subset of attributes. Every component is organized such that data items are represented within it in the same order.

Abstract: A facility for summarizing a set of data points each having a geographic location is described. The facility specifies the display of a map showing a geographic area the specified by a user. The facility identifies a number of geographic regions in the geographic area that are of a type that is automatically selected by the facility in response to the identity of the geographic area. The map indicates, for a least one of the identified geographic regions, information that summarizes one or more aspects of the data points of the set that have geographic locations contained in the identified geographic region.

Abstract: A facility for representing home attribute values for a plurality of homes and a plurality of home attributes is described. The facility incorporates a data structure comprising, for each of the plurality of homes, for each of the plurality of attribute value sources, the capacity to store values for any of the plurality of home attributes obtained from the attribute value source.