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Where Does The Blue Dot Come From?

Our guest today is Ed Parsons, Google’s Geospatial Technologist of 15 years. He is also a Director to the Open Geospatial Consortium, and a frequent university lecturer on geospatial technologies. Parsons studied Geography at Kingston University, and got his MSc in applied remote sensing at Cranfield University. Starting out in academia, he transitioned to the private sector by working for the National Mapping Agency, as well as a few smaller roles before moving to Google, where he has stayed ever since.

What is the Blue Dot on the Map?

To put it simply, the blue dot is you. To put it less simply,

the blue dot is your device’s predicted location based on the results of some unseen algorithms intertwined with the results of a set of fused location services.

In the early days of web mapping services, the web maps were essentially just digitized printed maps, and they had pretty limited features when it came to positioning.

Everything changed, however, when computers got smaller and more mobile. They became so mobile, in fact, that they could move with us. The hardware and software to make individual location services happen had developed, and now the masses can, in the click of an icon, put themselves on the map. Mapping services such as Google Maps, Apple Maps, Waze, and countless others have made this utility ubiquitous to the point where we don’t have to think much about it. When we do think about it, most assume the blue dot is GPS. This is a common misconception, so let’s get into why.

An important piece of housekeeping, what people generally call GPS, is better-termed GNSS, a global navigation satellite system. It is the generic term for a group of satellites (a constellation) that send positioning and timing signals to earth. Every GPS is a GNSS, but not every GNSS is GPS. GPS is a US-centric system, with the official name being NAVSTAR. Other countries have their own GNSSs. Russia has GLONASS, China has BeiDou, and the EU has GALILEO.

Fused Location Services

A fused location service is a location service that builds a result based on combining spatial information from multiple sources. For mobile devices, there are three elements that generally contribute to the blue dot.

  1. The Phone– Your cell phone is an advanced piece of technology which is capable of far more than just texting and Candy Crush.  Phones need to be aware of their location to enable their most simple functionality, sending and receiving calls. A phone needs to be able to find the closest cell tower to itself and then the closest tower to the recipient in order to complete the connection. This coarse level of location information is a great start for narrowing down where exactly the device is.
  2. WiFi Hotspots– The internet is nearly everywhere in this day and age, and this creates a geospatial advantage as WiFi hotspots have their own location information that can be broadcasted and used by other devices. Each router has a unique ID via the MAC (media access control) address. Their location information is built into massive databases which can be cached and queried based on the local geography of the mobile device in order to further narrow down its location. The caching element is especially helpful as it allows minimal network involvement, especially if you are generally staying in the same area.
  3. GPS/GNSS– So, GPS is involved to a degree with fused location services. Considering that GPS is very taxing on machine resources, resulting in drastically reduced battery life, the goal is to minimize its role as much as possible. Furthermore, GPS needs a clear horizon to the responding satellites to produce the most accurate location, and this is not a common scenario for most use cases.

Generally, most of the grunt work for fused location services is being handled through WiFi hotspots. It would be impossible to deduce this just from scrolling around your favorite mapping app, as fused location service management is handled on the OS-level of your device. This is perfectly fine, as there is no reason to be manually involved in this process. The closest use case for this would be as an application developer. In development, there are some options that can be controlled to manage the level of precision needed for a location measurement in the app.

How Accurate is My Location?

Of course, accuracy and precision are two different things. As a quick review, accuracy is how close the result is to the true value, while precision is how close the results are to each other. Ideally, we want a result that is both precise and accurate. If you have spent enough time using navigation applications, you know that they work splendidly 99.9% of the time, but it is that 0.1% we are going to dig into a bit more.

We must remember that GPS is the most accurate and precise data source we can use to find our location, but battery consumption and the ideal hardware carry a high expense. This means location calculation is mostly handled by interpreting cell tower ranges, and WiFi hotspots. Both of these methods are less precise than GPS, but realistically, for most use cases this does not matter. If you are looking to pull a weather report for your neighborhood, your exact XY location to the nth degree is not needed, close enough is good enough.

Consider this, go to your favorite fast food chain’s website. There will likely be an option to Find a Location Near You. When you use this tool, you should be able to search based only on ZIP code, and you will get a list of usable results, relevant to your geography. Providing your exact address here would be overkill. Keep this in mind the next time you download an application that requests your location, chances are, it does not really need it.

Location information is highly private, and sensitive. Reputable vendors, such as Google, will never share your location information with third parties for exactly this reason. They also avoid storing any of this data long term for security (and data storage cost) reasons. Additionally, they take measures to separate your identity from your reported location, further reducing the risk of such information being used maliciously.

Finding Locations in Cities

Man made environments provide a special challenge for navigation. They are full of thick concrete, metals, and competing network resources, introducing opportunities for error.

If you have ever opened your mapping application, and it briefly shows your blue dot as being in some exotic location, such as Birmingham, chances are it has picked up a stale WiFi hotspot from that cached database we mentioned before. The algorithms driving the fused location services will pick up that one of these things is not like the other, and discard the red herring.

Another common issue is with subways and metros. If you are deep underground, zipping along in an electric train, there is a lot of interference going on with your mobile device’s location tools, assuming it gets any connection at all. Once you emerge above ground, your phone comes out of this darkness into the light, but has no background information to kickstart its wayfinding. It will scramble to give your blue dot its location, but it has the further challenge of determining your heading/direction. This is where you get people on the sidewalk spinning in cute circles trying to follow the erratic arrow trying to direct them to the nearest street corner.

Google has made strides in attacking this issue by integrating VPS- a visual positioning system. This takes advantage of your phone’s camera, as well as the vast database of spatial and structural information that Google has stored about the earth’s surface in order to pull key points from the environment to help orient you.  They have even integrated augmented reality visuals to give you directions through your camera.

About the Author
I'm Daniel O'Donohue, the voice and creator behind The MapScaping Podcast ( A podcast for the geospatial community ). With a professional background as a geospatial specialist, I've spent years harnessing the power of spatial to unravel the complexities of our world, one layer at a time.