The issue with navigation charts
- They do not offer visual clues as to how the location will actually look like. So they are great for ...well...navigation, but are somewhat lacking when it comes to planning a route and choosing among a number of potential destinations along the way.
- They are sometimes not up to date: new structures (dock, bridges etc) may have been added since the chart was last updated.
- In some cases, they may not be 100% accurate.
Complementing navigation charts with Google Maps
While not designed for navigation, Google Maps are becoming an important compendium to route planning, working side by side with traditional navigation charts. Satellite imaging provides a great way to see how our destination actually looks like: how wide is the beach by the anchorage? Is the land covered in vegetation? Are there any unsightly buildings or industrial facilities in plain view from the anchorage?Of course, we could always fire up our browser and go to maps.google.com to take a look. But what if we have no Internet access, as in most cases when cruising?
Enter a new feature in squidd.io: downloading google satellite images for any of the thousands of destinations in a format that is compatible with OpenCPN, and can be viewed offline and superimposed to other raster (.kap) navigation charts. Maps can be downloaded at different levels of zoom: from highly detailed small scale charts for a specific marina or anchorage, to large scale charts covering entire regions.
How to import Google Maps into OpenCPN
Downloading and importing a Google Map into OpenCPN in .kap format is extremely easy:- Navigate to the location you are interested in on sQuidd.io. (for instance, the Treasure Island anchorage shown in the image above, in the San Francisco Bay) . I find it very convenient to do this directly from within OpenCPN using the squiddio plugin.
- On the Google chart, select the level of zoom you need for the chart. I normally download a high-definition 1 x 1 nautical mile chart covering the anchorage, and a larger, say, 6 x 6 NM lower definition chart covering the vicinity. If your itinerary covers multiple destinations, you can create a patchwork of different charts so that the entire area is covered at different levels of zoom. Use the + and - control on the Google map to adjust the level of zoom. See the table below for indicative chart sizes relative to their Google Maps zoom level.
- Click on the download chart button, right below the map in the destination page. In a second or two your .kap file will be available on your hard drive.
- Copy the file (or files) to your OpenCPN chart directory (go to Settings/Charts to find the directories OpenCPN is using). I use Chart Groups extensively to organize my charts in OpenCPN, so I have created a specific group for Google Satellite Maps, which are saved to a directory contained within raster chart directory. This way I can view only and all the Google charts I have downloaded, or view them "quilted" with the other raster charts (which is useful when wanting to assess the accuracy of old raster charts).
- Update the chart database in OpenCPN (again, Settings->Charts->Scan Charts and Update Database).
| Zoom Level | Approximate Area covered by chart (NM) |
| 15 | 1 x 1 |
| 12 | 11 x 11 |
| 10 | 44 x 44 |
Happy route-planning!

