PIHMgis demonstrates an integration methodology for an open source GIS framework and a integrated hydrologic model that enables users to take advantage of object oriented computer programming (OOP) to provide more direct access to the GIS data structure to better support efficient query and data transfer between the hydrologic model and GIS. The data structure has been designed to be flexible for modification and customization of the model or GIS, rich enough to represent complex user defined spatial relations and extensible to add more software tools as need be. The “tightly-coupled” integrated GIS interface to Penn State Integrated Hydrologic Model (PIHM) has been created in the Open Source Quantum GIS.

Modularity is achieved via the plugin architecture which provides a mechanism for third parties to extend the QGIS core application while maintaining independent development paths. QGIS has a simple plugin mechanism that can be used to add new functionality to QGIS without needing to modify the core source code. Users can write-in plugins to add additional functionality (models, special viewers, hot-link handlers, data editors, etc.) and pass these along to any number of clients and end users. PIHMgis is an external plugin to QGIS with an independent build system in order to maximize flexibility in using and extending the software.