We all know that nautical charts are the primary source of depth information for navigators, but what about Google?
Google Maps and Google Earth both show an incredible amount of information. You find maps, satellite imagery, traffic information and even photographs of the entire world through Street View.
So, what about the ocean?
It turns out, Google does give us information about that as well.
Google Earth shows water depth, but Google Maps does not. With Google Earth, you can hover your cursor over any point across the world’s oceans and it will tell you the depth in meters. It is not accurate enough for navigation, but it does allow you to explore the ocean floor.
Google Earth is Google’s exploration application, useful for users to explore unfamiliar areas. It is different to Google Maps which is designed more for everyday use as a navigational tool.
In Google Earth, you get to explore the world through higher resolution satellite imagery than you will find in Google Maps. Google Earth also includes 3D rendering of its satellite data, giving you a much better understanding of the topography of the terrain.
In terms of oceanic data, Google has enough to provide an exploration experience, but they do not have enough to create a navigational tool.
Their data is detailed enough to generate topographical renderings, and provide sufficient resolution for the exploration experience in Google Earth.
They do not, however, hold enough data to generate a map (or chart) that would be of a high enough resolution for navigators to use on boats or ships.
For that, you still need to rely on official electronic or paper charts produced using data from national hydrographic organisations.
How do I see water depth using Google Earth?
To find water depth using Google Earth, you can either use the application on its own, or you can just open Google Earth in a web browser.
I found it worked best in Chrome. Other web browsers showed the depth in shallower areas but stopped showing it for deeper parts of the ocean.
Once Google Earth is open, just pan across to any point on the ocean that you want to explore and hover your cursor over the point that you want to measure.
Pro Tip: Search for the Mariana Trench if you want to explore the deepest part of the world’s ocean.
Once you have positioned your cursor, in the bottom right of the screen you will see the elevation, in meters.
As you are over the ocean, the elevation will be negative, indicating that it is giving you a measurement below sea level.
Note: If you do not see the water depth, you might need to zoom in a little closer. I found it did not measure if the camera was above 2000km.
Can you get depth information on Google Maps?
Although you cannot directly read depth information from Google Maps, with a little creativity you can find some clues.
The first step is to switch Google Maps to use its satellite image layer. The map above shows the satellite image of a part of Sydney Harbour.
We can then look for clues in the colour of the water, and the vessels that are around.
You can see ripples surrounding the boats on the pontoons, indicating that the water surrounding them is at least deep enough for them to float.
Notice also how the seabed near to the pontoons themselves looks like it shallows up a little. This indicates that the area just outside of the boats is slightly deeper, so I would assume a few meters at least.
The next thing you can notice is the sunken vessel near the beach. If you look carefully, it is not clear whether the vessel is actually underwater, or whether it is just a cropping issue from stitching photos together.
Unfortunately, you cannot gain much information from that one.
The final clue in our initial investigation is the small boats that are clearly at anchor. You can see that they have been swinging on their moorings as they are in two different positions once images are stitched together.
Again, as they are safely at anchor you can assume that the water is at least a few meters deep so they are all floating.
While it is possible to find clues about the water depth, you can already see that the information is not even close to being good enough for navigation.
For that, instead, we need to turn to something different, a nautical chart.
Nautical charts give accurate depth information, and when you check the chart for this area of Sydney Harbour, you find that the depths start around 11m, and gradually slope in towards the shore.
I cannot include an image for copyright reasons, but you can see it on the Navionics Web App for yourself.
Is there a Google Maps for the ocean?
Google Maps is great for navigating on the land, but it does not have sufficient data for navigation at sea.
There are a few other websites, however, that do contain a great deal of information. Effectively, these are the Google Maps for the ocean.
You can read a full comparison of these apps in my other article: Top 5 Boating Equivalents To Google Maps
The Navionics Web App is a free online version of the Navionics charts that you would find on a boat’s chart plotter.
It is not to be used for navigation, but if you want to browse around and see the navigational marks and depth contours that vessels would use, it is a great option.
C-Map Chart Explorer gives you a free way of exploring their worldwide charts.
There is not as much control or detail as their actual charts, but for a general overview of navigational features, it gives you all you need.
You can even turn on “Shaded Relief” which adds different colour shading to different depths of water.
The relief view of the Mariana Trench really gives you a great impression of its overall depth and scale.
i-Boating is another great example of a free online nautical chart, although some areas of the world are missing.
Unlike the other options, i-Boating seems to stitch together data from different sources so you will find some vector areas and some raster areas all on the same chart.
OpenSeaMap is a creative commons project that is aiming to produce the equivalent of a Google Maps for the ocean.
It is available to use under a Creative Commons – Attribution – ShareAlike license which really opens up creative options for anyone wanting to use nautical maps in a project.
The map is not as detailed as the other ones on my list, but the CC license is enough for it to make my list.
While not strictly similar to Google Maps for the ocean, you can get actual nautical charts for free from the NOAA website.
The charts are available in .pdf format, so you can download and browse a small area at a time.
Is there an app that shows water depths?
There are plenty of apps that will show you water depths, however, most of them are not free.
Downloading an app that shows water depths effectively turns your phone or tablet into a chart plotter.
I have extensively reviewed different chart plotter apps, so you can read a great deal more detail in each individual review.
Otherwise, check out my comparison of the Top 8 Apps For Marine Navigation.
My top choice is the best-designed app for using your phone or tablet as a chart plotter.
Full review: Navionics Review
iSailor is the most technically advanced app, and the most similar to commercial systems that I have used on large ships.
Full review: iSailor Review
C-Map is the best value app on my list. It gives you free access to worldwide charts, so you can check out water depths across the world as long as you have an internet connection.
Full Review: C-Map Review
iNavX is an incredibly customisable nautical charting app that can display data from lots of different sources.
Full Review: iNavX Review
Seapilot is another excellent chart plotter app that is very similar to systems that I have used on commercial vessels.
Full Review: Seapilot Review
Why doesn’t Google Maps show water depth?
We have already established that there are lots of alternatives to Google Maps that do show water depth, so why is the information not available on Google Maps?
The main reason is due to the copyright of data.
Google has a lot of resources at its disposal, but even they cannot compete with hundreds of years of governmental surveys of the seabed around the world.
Surveying the seabed is an incredibly expensive and labour-intensive task, requiring ships to literally scan above every part of the ocean.
Each of those ships needs to be built, equipped, crewed and continuously replenished with fuel and supplies.
The US Navy, for example, has a fleet of survey ships that it uses to conduct oceanographic research as well as geophysical surveys.
Despite its resources, even the US Navy cannot map the entire seabed.
Instead, to create commercial charts for navigation, companies license data from hydrographic offices around the world.
Navionics, for example, has an acknowledgement page of over 4000 words, which lists all the different data sources that they draw on.
Most of those data sources charge a license fee for the use of their data. When you purchase charts from Navionics, you are indirectly financing the surveys that produce the data you use.
If google was to make all that data publicly available, I assume there would be astronomical licensing fees that just would not be commercially viable for the number of users that it would benefit.
As technology develops, and data becomes easier to obtain, I am sure Google will introduce a maritime version of Google Maps.
Until then though, we can use the commercial options that I have listed above.
How accurate is water depth in Google Earth?
Water depth is Google Earth is accurate enough for general exploring, but nowhere near accurate enough for navigation with a seagoing vessel.
In an area of sea that I am intimately familiar with, Google Earth gives depths anywhere between 1m and 20m, when I know the depth is around 10m.
This is only an issue when you are looking for very precise data, such as is necessary when you are navigating a ship with an 8m draft.
When you are just interested in general observation, there is no issue.
For example, the Great Abyssal Plain off Biscay is charted anywhere between 4000m and 6000m deep.
Google Earth gives similar numbers, but of course, at that sort of scale, it really doesn’t matter if there is even a 1000m discrepancy in the readings.
Challenger Deep shows up on Google Earth at approximately the same depth that it is recorded, near 11,000m.
The thing with Google Earth is that the resolution is not high enough to be too precise.
According to earthsky.org, in 2011 Google Earth released an update that shows 5% of the ocean’s seafloor at a resolution of about 100m.
Even if 100% coverage at 100m resolution was achieved, this only means that there is one sounding taken in any 100m.
That is plenty accurate enough for general observations. You will still be able to see ocean trenches, mountain ranges, and abyssal plains.
For navigation, however, it is nowhere near accurate enough.