Different scales of data are more appropriate for different types of applications. Some digital data layers are generated from an existing analogue (hard copy) data source. These analogue data sources are associated with different map scales. For example, local parcel data are often developed at a 1:600 scale, while topographic maps are collected at a 1:24,000 scale. You could not use a topographic map to accurately develop a parcel data layer, as too much information and accuracy is "lost" at the smaller scale.
Accuracy levels are often associated with scales. The National Map Accuracy Standard (NMAS) was developed by the U.S. Bureau of the Budget (1947) to standardize accuracy levels of spatial data. Thus, certain applications (such as surveying/parcel management/floodplain delineation) that require a higher level of accuracy need to be associated with larger scale data layers (i.e., 1:1,200/1:2,400) that were generated in compliance with NMAS.
Read more about Map Accuracy and Scale at FAQ 29912.
It should be noted that while a GIS will enable you to zoom in (and out), the accuracy of the data does not improve as you change display scales. The accuracy of your GIS data is limited to the accuracy and the scale of the source data it was derived from, not the zoom level at which you view the data. This is especially important to consider when working with vector data sets since points, lines, and polygons will never look pixelated, even when zoomed in past the scale at which the data are meant to be used (unlike raster data, which show more and more evidence of pixels as you zoom in).
