The orthophotos have delivered a new standard for spatial accuracy. By overlaying existing vector GIS data with orthophotos, spatial errors in our vector GIS data are quite apparent. Suddenly, spatial errors in our GIS database that were both unknown and of no concern are all too visible to laymen and experts alike.
This is a good time to (re)read our disclaimer which talks about inaccuracies that are inherent in our GIS data.
Orthophotos are available both on our "Main MapGuide Map" and the "Orthophoto Map" on our primary MapGuide page.
We know the vector and point layers aren't perfectly registered with the orthophoto image. Where there are positional differences, the orthophotos are substantially more accurate spatially. See "What We are Doing About Spatial Errors" below.
The exception to this is the Geodetic Control Points layer which is quite accurately registered to the orthophotos. Be aware that these control points are not section corners and are not necessarily aligned with section corners. In other words, the control points may not appear to be in the "right" place, but probably are. This and more is explained on the Geodetic Control Points page. Further, because the section grid is based on various sources and other spatial errors, the section grid layer may not be entirely accurate on the orthophoto map.
Our GIS database was developed prior to availability of orthophotos and was never intended to be perfectly accurate. This is close to impossible with GIS.
When data is entered into a GIS system, there are tradeoffs between accuracy, cost, sources of information, and the intended use of the data. Our GIS database is a planning database that shows relationships accurately with features registered and located as well as possible within the constraints at the time the data was entered -- and our GIS data library has been built continuously since 1988. Everyone wants the data to be accurate within inches, but as a practical matter this is too expensive and not needed by virtually all the users of the data.
When more accuracy is needed our GIS data is linked to source documents such as Subdivision Plat Maps, Assessor Record Maps, or construction plans that may provide more accurate spatial geometry within limited areas.
On the other hand, it's possible you are seeing errors we aren't aware of.
If this explanation doesn't adequately explain errors you are seeing, then please let us know what is wrong in more detail.
Certainly there are errors that have nothing to do with spatial accuracy concerns.
We want to know about these errors and fix them.
Send e-mail to 
describing
the location and nature of the error(s) you see.
We have a large ongoing project to rectify all our GIS data layers with the orthophotos. Rather than moving individual map features, we develop offsets from certain known points on the orthophotos and apply those offsets to our vector data.
Unfortunately, parcel boundaries are not necessarily visible in the orthophotos as there may not be anything physical (or at least anything visible) defining the boundary. Even where a boundary such as a fence can be seen, it may not represent the legal boundary. Further, street pavement borders are usually not representative of the right-of-way.
Within these limitations, we manually generate correction vectors to register the parcel layer with the orthophotos.
We are using these corrections developed for the parcel layer to correct virtually all our other layers. This will greatly improve the registration of our entire vector GIS library with the orthophotos. However, even after this process, layers will still have spatial and other errors created during their original entry. Furthermore, corrections will apply only to areas with orthophotos.
As additional orthophotography becomes available in new areas, we are using it to correct the vector GIS data in those new areas. We are also doing manual refinement where needed.
Spatially correcting our vector layers is an ongoing project of continuous refinement.