Data Set Description:
Parcels delineate the boundaries of property ownership as recognized by the County of Alameda. Each parcel has at least one Assessor's Parcel Number that is its unique identifier within the county. This number is the link to various City of Oakland databases containing parcel information such as owner name and address, property value, and land use. There are approximately 103,000 parcels in the City of Oakland. Because of the large size of this dataset, the original coverage has been subdivided into 50 (??) smaller tiles containing between 2000 and 5000 parcels each. These smaller tiles comform to planning area boundaries and are stored in an Arc/Info library system.
Non-standard Attributes in table:
- APN= Assessor's Parcel Number.
- Note: If you are using the shapefile versions of the parcel dataset, they are divided into 12 different files coded as follows to fit into planning areas (see planarea GIS layer): parcai*.shp = Airport, parccc*.shp = Chinatown Central, parcce*.shp = Central East, parceh*.shp = Elmhurst, parcfr*.shp = Fruitvale, parcha*.shp = Harbor, parclh*.shp = Lower Hills, parcnh*.shp = North Hills, parcno*.shp = North Oakland, parcsa*.shp = San Antonio, parcsh*.shp = South Hills, parcwo*.shp = West Oakland.
Data Source History:
Geometry: The first source of geometry was EBMUD digital files based upon EBMUD records. Upon examination, these files were revealed to be only 65% complete. Robyn Starr, an independent consultant, was contracted by the OCIS to correct the EBMUD parcels by referring to Office of Planning and Building (OPB) records. Robyn obtained paper maps of parcel boundaries from OPB. They were of various scales, each displaying one planning area and all its parcels on a 3 x 4 foot page. Robyn Starr scanned portions of these paper maps in an overlapping tile arrangement. He then registered and rectified each scanned image using the street centerlines GIS coverage to derive control points. He then corrected the EBMUD lines to match the lines in these scanned images, closing all formerly open parcels and adding or removing lines as necessary. The end result was a series of 12 coverages, one for each planning area, with one closed polygon per parcel.
Further corrections to the geometry occurred during establishment of the parcel library. Julia Howlett, JRH Consulting, created tiles based upon planning area boundary subdivisions that divided the original 12 planning areas into smaller units, each containing between 2000 and 5000 polygons apiece. During this process, she discovered parcels that had been improperly split by the original planning area divisions; she corrected these errors by referring to Assessor's Map Book pages, which she scanned, registered, and rectified, as described above.
Attributes: Each parcel has (potentially) as many as 150 different attributes. These are captured by the county assessor, by municipalities, and by special projects. All of these attributes can be referenced via the Assessor's Parcel Number (APN). To assign this critical reference number to all 100,000+ polygons in the dataset, Local Knowledge Consulting retained five independent sub-contractors who entered each APN manually using the assessor's map book pages as a reference and ArcView as a data-entry tool. The work was performed at OPB, with Joan Curtis and Thomas Casey as sources of information when APN assignment was ambiguous. Julia Howlett, JRH Consulting, managed the bulk of this data-conversion effort which lasted nine weeks.
After APN data entry was complete, additional data such as the owner name and address of each parcel was joined to the parcels using Arc/Info's JOINITEM command. The additional data was supplied by David Rodrigues (OCIS) from the PTS system and MetroScan.
One automated quality control step is planned to insure that the geometry and its APN assignments are correct. It is: to compare the complete APN list from the GIS parcel layer with the complete APN list from Alameda County Assessor's office. The comparison will reveal which APN's are absent from the GIS parcels. The eventual goal is for a perfect match. Julia Howlett completed this first quality control step. She discovered that approximately 20,000 of the 104,000 APN's were missing from the GIS parcels layer.
Still remaining is the need for an ongoing manual update to the geometry of parcels that have been split or changed. Also necessary is the creation of an associative table of multiple APNs in the same vertical parcel space, such as is the case in high-rise condominiums. The system needed for implementing this associative table will be in place by June, 1997.
No security restrictions
Geometry: Yearly (as assessor updates map book pages)Attributes: Quarterly (January, April, July, & October)
The data supplier sends OPB updated Assessor's Parcel maps on CD ROM approximately every two weeks. Tiff images on the CD ROM are registered and rectified to a mapbook grid and laid under the parcels coverage as a guide for edits. Edits by an OPB GIS resource are made one mapbook at a time by clipping along the tile boundary and being placed back into the tile structure when complete.