How often is Google Maps updated?
The images in Google Maps (and Google Earth) are updated on a continuous basis. The update cycle is typically twice a month, but only a handful of areas are updated at a given time. Updates are made when new imagery is available from a variety of sources.
It's hard to say exactly when an area will be updated because some areas may be updated more frequently than others (just because that data is more readily available). While most images are no more than 3 years old in high resolution areas, low resolution imagery in some areas may be older.
Due to overwhelming demand when a given area will be updated Google has created a new e-mail notification service. Check out 'Follow Your World' in related links below.