An API -- application programming interface-- is a way for a person or a group of people to access functionality of a software or hardware platform in order to build their own applications. The Kaleidocade Indicators Framework (KIF) API provides a webservice enabling administrative users to embed query results-- such as dynamically updated maps-- in other web applications.

Geocoding refers to the GIS operation that assigns latitude and longitude coordinates to a geographic reference (street address, location-based data, etc.), which can then be displayed as a feature on a map or used for analytical purposes, such as identifying corresponding geographies like census tracts or police districts. KIF uses geocoding to simplify the data retrieval process by enabling users to enter an address and be provided with a list of matching data sets from which to build indicator collections. KIF's framework is built flexibly so that clients can employ the geocoding service that is best suited to their needs.

The census tract is one of the most commonly employed levels of geographical analysis, for several reasons. The boundaries of tracts are intended to be relatively permanent, making them a stable unit for tabulating and comparing census data across years. Tracts are subdivisions of counties or county equivalents and their boundaries typically follow permanent, visible features, such as streets, roads, highways, rivers, canals, railroads, and powerlines. The population within a census tract is meant to represent a relatively homogeneous group, ideally comprising about 4,000 people and 1,500 housing units. There are approximately 50,000 census tracts in the U.S., each represented by a 4-digit number and an optional 2-digit suffix that is appended when population changes necessitate that a single tract is subdivided into new tracts.

Census block groups are subdivisions of census tracts, and are the smallest unit for which the Census Bureau publishes sample data-- data that is collected from only a fraction of households. Block groups are identified by a single digit that appears as the first number in the ID of blocks located within it. There are roughly 210,000 block groups in the United States, with an optimum size of 1,500 people.

The census block is the finest scale at which the U.S. Census Bureau releases 100-percent population data-- data collected from every household. As implied by their name, blocks frequently correspond to city blocks in urban areas, but in less densely populated areas may be bounded by streets, streams or the boundaries of other legal or statistical entities. Blocks are identified by a 4-digit number, where the first digit represents the block group in which it is located. There are approximately 39 blocks per block group, with a total of 8.2 million blocks in the United States. The population of census blocks varies widely.

Geographic aggregation is the process of summarizing spatial data by larger areal units. Often, data is collected as points or addresses-- think of the locations of crime incidents or the households surveyed in the decennial census-- but is only made available to the public in aggregated form, as summary statistics at the level of police precincts, census tracts or even counties. This may be done to preserve confidentiality so that individuals are not identifiable or simply to cut down on data management costs. To simplify the process of creating reports within KIF, users are asked to select a geographic area of interest and the data available at that level of aggregation are made available. KIF does provide some simple analysis functions that allow users to assemble data from existing geographies, such as searches within a given radius or visual overlay of alternate boundaries.

The Modifiable Areal Unit Problem (MAUP) characterizes a potential source of error when spatial data is aggregated to bounded areal units, such as census tracts or police districts. Because the data in question are generally points distributed over space, if the zones of aggregation (our "areal units") are drawn differently (that is, they are arbitrarily "modifiable"), then substantially different patterns may emerge. These patterns may simply be artifacts of the aggregation process; alternately, real patterns in the data may be obscured by the process of aggregation. Unfortunately, researchers are often constrained by the geographic scale at which data is available (see Geographical Aggregation).