Here you go ... I found this (you can tell I am bored today!! Horray for RIBnet)
What's the difference between VECTOR and RASTER electronic charting?
There are two very different technologies used in electronic charting, and they are not interchangeable. Most chart plotters (like those from Magellan, Garmin, some Northstar models, and others) use vector charts, which bear little resemblance to regular paper charts, but have some real advantages.
In essence, VECTOR charts are a rendering of a lithographic chart in a point-by-point format. They allow you to zoom in to large magnifications without distortion. As a rule, the hardware that uses this technology is all-in-one units (aqua. chartplotters) that include a screen, a GPS, and a programmable interface. All you add are the chart cartridges. Vector chart plotters generally cost between $500 and $2,000+. Vector chart cartridges (of which Navionics and C-MAP NT cartridges are examples) cost more, some time substantially more, than similar coverage on raster chart CDs.
The alternative RASTER charts, are digital scans of printed lithographic charts. They are produced by companies like Maptech and NDI, and they look identical to paper charts, because they are pictures of them! They cannot be zoomed in to very high magnifications without losing sharpness. They also require the considerable computing power of a laptop or onboard computer to display the charts and drive the navigation software. All in all, raster charting systems require is a larger investment in technology than vector charting systems. However (and it's a big however), having a computer onboard opens a floodgate of opportunities, such as e-mail and fax communications, weather data, and more -- not to mention word processing, games, internet, and all the rest that goes with a computer.