The datum for this project is NAD 83 (1998) for horizontal location and NAVD 1988 for vertical. The County GIS system is based upon the County Surveyor's current datum. The County Surveyor's office considers any datum other than NAD 83 (1998) to be superseded data.
Use of superseded data is strongly discouraged. However, we recognize that it is needed for vertical control related to Flood Plain work in areas where the FEMA maps have not been updated to NAVD 1988.
It has come to our attention, that some jurisdictions in Clackamas County are requesting professional surveyors perform work to other standards. If you are aware of this type of practice, we would ask you to provide us with particulars so we may contact the jurisdiction to determine if we can all work toward the same datum base.
For your information, all superseded GPS Records have been moved from our public research area to our vault. In the public file of the superseded record, you will find a note card to contact staff. This will allow us to encourage new work be performed to current standards, yet will allow the accessing of records when necessary.
Completed County Control Network Surveys
GPS projects completed and surveys are filed in Molalla (SN2004-117), Milwaukie (SN2004-356), Happy Valley (SN2005-084), Damascus (SN2007-167), and Alder Creek to Welches/Lolo Pass area, titled Hoodland Highway 26 (SN2006-280).
Current GPS Control Efforts
No network densification projects are scheduled. Currently, all GPS work is based upon using the ODOT Real Time Network (ORGN) and obtaining GPS derived data using the Oregon Coordinate Reference System (OCRS). Caution is needed when using the OCRS. Please pay particular attention to the OCRS zone that the coordinates are published for.