An Example
In Fiji, charts are reasonably accurate when entering major harbors used by commercial ships. When going to less-travelled islands, the locations of land areas are represented reasonably accurately but the positions of reefs were only somewhat related to their actual positions. Musket Cove is a popular anchorage in Fiji and while we were anchored there, a large catamaran grounded hard on a reef. They were lucky and sailed free on the next high tide. While it is recommended that you only sail reef-strewn areas in times of good lighting, this is not always possible.
Figure 1 shows the electronic chart of Musket Cove overlaid with the Google Maps satellite/aerial photograph. Notice that while the land is represented accurately on the chart, the reefs are only marginally accurate, particularly in the center where my anchor position is marked on a green reef. In actuality, I was in over 40 ft. of water in the center between the two reefs as shown by Google. In this case, Google is the more accurate position source.
Useful Techniques
For this application, go to Google Maps and use only the satellite image mode. You can change from street maps to satellite image with an icon in the lower left corner of Figure 2.
If you already have a waypoint or lat/lon information from a chart or chartplotter and want to see it in Google Maps, enter the coordinates directly into the Google Maps search box (“1” in the figure). Google Maps is quite forgiving about the format for input: A decimal-degrees input is shown but you can use degrees-minutes and put in a space for the degrees symbol like this: “17 46.623s 177 11.038e” and Maps takes you to that location and puts a marker there.