The three tier WebGIS architectural design pattern has three components, namely a
Data Management Component, a Computation and an Interaction component which
correspond to the well-known data tier, logic tier and presentation tier (Eckerson, 1995).
The data tier is represented by several distributed databases, the application tier is
represented by services for visualization and download and the presentation tier is
represented by the user interface. The fundamental characteristic of the three-tier
architecture is its linear topology and the clear communication interfaces between
components.