We have some maps in paper format and others already digitized. If you have to go through several source maps to convert a single element, more overhead time will be required during the actual conversion process. If possible, try to compile all of the information for a given element onto a single source, be it paper or digital. For example, if you are converting a manhole feature, pick an attribute that will differentiate it from another feature type. At the same time, you should create a way to distinguish one element of the same feature type from another element.
Raster is a format for storing and displaying graphic data as pixels.
Raster data is a single image comprised of no singular elements. A typical example of raster data is what you produce by scanning an image into your system. Street centerline data can contain address ranges, county names, and street names as well as zip code information. Additional project-specific attribute information can also be added to the street centerline data. The primary role of centerlines in a GIS is to help locate intersections, addresses or provide routing information by query.