Principles of Using Integrating GPS and GIS in Surveying of Displacement of Large Span Bridges Mohammad Hooshmandzadeh Department of Civil Engineering ,Islamic Azad University of Ahwaz branch ,Ahwaz,Islamic Republic of Iran, Iran Email: hooshmandzadeh_civil@yahoo.com A bridge database which has rough coordinates of bridges, was established and shared in a local government for the purpose of their maintenance. When bridges in the database overlaid with commonly used river and road data, they were not exist on near the intersections of roads and rivers. In previous studies, some bridges of bridge database were adjusted by using GIS data of rivers and road, and 23 bridges existed on a test area. It was possible to adjust the bridge database, but only 8 bridges were adjusted because of limitation of GIS in accuracy domain. In this study , only remote sensing data were used for the accuracy adjustment of the bridge database of the test area. River streams data and edge of bridges were needed to adjust the positional accuracy of the bridge database. River streams were extracted from ASTER images. And the edges of bridges were extracted from IKONOS images. The outsides of rivers on the edged IKONOS images were masked by the river data from ASTER images.Then the accurate bridge positions were obtained from the edge of bridges. 17 of 23 bridge’s positional accuracy were adjusted. Detailed information about the characteristic deflections of large structures such as bridges and tall buildings can help to determine the “health” of such a structure as well as to evaluate whethersuch deflections are the same as those that the structure was designed to tolerate. Due to the everincreasing size of some of these structures, a reliable and accurate health monitoring system could detect uncharacteristic vibrations and deflections, and help prevent disastrous consequences.The use of kinematic GPS has been shown on many occasions to be a viable tool for monitoring the deflections of large structures through its ability to provide cm level precision, at a rate of up to 10 Hz with real time capabilities and with the rover receiver being able to be positioned at a distance of up to ~20 km away from the reference (ideal for long bridges). GPS is limited partly by multipath and cycle slips as well as the need to have good satellite coverage, whilst accelerometers are limited due to the fact that their readings will drift with time.In this paper presents the principle of GPS in large span bridge surveying GPS satellite geometry and its impacts on bridge deflection monitoring,the principle of deck (of bridge )gemetry adjustment and 3. Coordinate Transformation and Attitude Determination for the Bridge Deck.