Orthophoto or Raster Imagery
Historical datasets are made available for your use for that layer by choosing the desired, available year in a drop down.
The earlier, older dataset's resolutions could be at a lower than one  meter. Regardless, it makes for an excellent resource if you are looking for anomalies that may be occurring or have the potential to occur. You may also want to use it as another reference for any indication of possible activity if you are managing land from afar.
There is also a Photo Date layer. This layer will label the date and year on the mapping interface. Mostly, when you are working on or near interstate boundaries [when you have land from two states in view on the mapping interface] the imagery can appear different and you may want or need to be able to enable the Photo Date layer.
The Hillshade is an adjustment layer to the NAIP imagery. It provides a visualization of the elevation changes by adding a shadowing effect.
Canadian Air Photo Mapping Imagery
For the two Canadian provinces, Manitoba and Saskatchewan, that we serve, the imagery will auto switch to "Air Photo". However, the imagery here is for a span of years such as 2008 - 2010. Otherwise the behavior, as far as having the latest imagery or being able to disable the imagery layer is the same as the U.S. land imagery.