Property boundaries are established though deeds, plats, ordinances, etc. These boundaries described in these documents do not always agree with one another.
Property lines are merely representations of what is on the ground.
The buildings are actually more accurate geographically than the property lines. Efforts are constantly being made to resolve discrepancies between the documents and improve the accuracy of the property lines. Due to the density of data within some layers, certain layers were set so that they appear only at certain scales. This was done so that the site would not be overwhelmed. If a layer does not appear simply zoom in or out until the layer does appear.