About Our Data

Data Projection, Accuracy, and Disclaimer

Data Projection
Coordinate System: State Plane Coordinate System Colorado Central Zone 3476
Projection: Lambert Conformal Conic
Units: Feet
Datum: NAD83
Spheriod: GRS1980

Data Disclaimer
The information in the City of Aspen/Pitkin County's GIS products was derived from a database that is maintained by the GIS workgroup. While care is taken in the creation and maintenance of this data, the City of Aspen and Pitkin County cannot accept any responsibility for errors or omissions. There are no warranties, expressed or implied, that accompany this product. However, notification of any errors is be appreciated.

Data Accuracy
The Aspen/Pitkin GIS database was initially created in 1991 based on digitized aerial photography. Planimetric features illustrating natural and man-made features were captured for approximately 25% of the County.

Area	Photo Scale	Date
Roaring Fork Valley	1:24,000	June 24, 1991
Crystal River Valley	1:24,000	May 29, 1991
Aspen Metro Area	1:6,000	May 17, 1991

Planimetric features for the remaining portion of the County (approximately 75%) were obtained from USGS digital line graph (DLG) and digital raster graphics (DRG) datasets.

Subsequent to the initial base data creation, several other aerial flyover projects have commenced in the County. After each flyover, GIS staff has updated various planimetric feature layers.

Area	Photo Scale	Date
Aspen Metro Area	1:8,400	Oct 19, 1997
USGS–(location varies) Digital Ortho Quarter Quads	1:40,000	1993-1999
Roaring Fork Valley	1:18,000	May 12 & 14, 2003
Crystal River Valley	1:18,000	May 12, 2003
Meredith/Thomasville	1:18,000	May 12, 2003
Redstone	1:7,200	May 12, 2003
Aspen Metro Area	1:1,500	April 27 & May 3, 2004
Aspen Metro Area	1:4,513	Oct 26 & 27, 2008
Pitkin County Lower Elevations	1:4,800	June 7-10, 2010
Pitkin County Higher Elevations	1:6,000	June 18 &19, 2010

Most of the thematic layers, representing subdivisions, taxing districts, administrative boundaries, zoning and similar themes, were built using the parcel layer as a base and therefore inherit the accuracy of the parcel layer. The accuracy of the parcel layer varies with the method used to capture the data. Recorded plats and subdivisions were entered using coordinate geometry (GOGO) while all other properties were digitized. Fifty percent of the parcels in Pitkin County were entered using COGO.

Below is a more detailed description of the input methods and the accuracy obtained.

Cogoed Areas:
Location information (coordinates) for section and quarter corners were obtained using public land survey data from the BLM. These corners were used as control for the cogoed parcel boundaries. The source documents include recorded deeds, subdivision plats, and surveys. Information from the source documents (using bearings and distances) were entered into the GIS. As discrepancies were found, adjustments were made so that the parcels fit the control and each other.