Electronic Charts
Screenshot comparing raster and vector charts. Navigation software is useless without electronic charts. In the early days of the industry, electronic chart coverage was incomplete and a few manufacturers dominated chart production. Much has changed today—there is chart coverage for most of the world and many firms produce charts. There are two different types of charts available for navigation software programs—raster and vector charts.

Raster charts are simply digital "pictures" of a paper chart. Raster charts are somewhat similar to the jpeg images that many digital cameras take. The primary advantage of a raster chart is that what you see on your screen is exactly what you would see on the equivalent paper chart. For people who are comfortable with paper charts, this is a significant advantage. However, there are a couple disadvantages to raster charts. One disadvantage is the relatively large file size of a raster chart. As a result, the chart takes up more space on a hard drive and slows scrolling and zooming operations. Another disadvantage is chart clarity. When raster charts are displayed at something other than their native resolution and orientation, they can look non-optimal.

Unlike raster charts, vector charts are mathematical equations that represent the original data on a chart. These mathematical equations are driven by information stored in an underlying database. Consequently, vector charts are not exact pictures of the original charts, but representations of them. The primary disadvantage of vector charts is just that—if you are used to paper charts, vector charts may look somewhat unfamiliar. Vector charts also inherited a reputation of lacking detail. This reputation comes from early plotters, whose vector charts were fairly simple. Vector charts used in modern navigation software programs (and in many cases designated plotters) have improved significantly in recent years. In terms of nav-aids and water features, you will find vector charts are every bit as detailed as their raster cousins. Due to their architecture, vector charts take up much less space on a hard drive and also scroll and zoom faster than raster charts. Vector charts also do not suffer from clarity problems. Vector cartography will maintain clarity regardless of scale or orientation. Finally, vector charts have the added benefit in that they are created in layers and have an inherent "intelligence" due to their reliance on an underlying database. This means you can turn on/off different layers and display navigation data in creative ways.

Both raster and vector chart manufacturers have recently started including additional data with their basic chart packages. In addition to getting basic cartography for a given region, the manufacturers are throwing in other data like aerial photography, street and road atlases, extensive bathometry data, US Geological Survey topographic maps, coast pilots, marine facilities and more.



[On to Reduced Reliance on Paper Charts]





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