Go to Google Maps and take a look at a township in South Africa, a slum in India or a favela in Brazil. The website will show you a few roads, surrounded by plenty of blank space.
Now switch to satellite view, and you'll discover teeming cityscapes, bustling with life in unmapped houses and businesses, along hundreds of uncharted streets. Or check out Libreville, Gabon, where you will see many roads, but the streets have no names.
Yes, often these are places of shocking deprivation. However, they also hold huge economic potential, harbouring an emerging middle class that is working hard to lift itself out of poverty. Economists estimate that three billion people could join the middle class during the next 15 years. It would be the biggest and most dramatic decline in global poverty yet.
However, three hurdles stand in their way: they are unconnected, unbanked and unaddressed.
1.Connectivity is obviously the easiest problem to solve. The rapid uptake of mobile phones, especially smartphones, is taking care of that. Today, Indian fishermen still at sea can find out which harbour offers the best price for their catch; farmers in Uganda go online to get help tackling crop pests; and in Chile, mobile phones are fuelling a thriving scene of online start-ups.
2.Providing access to financial services is a much bigger challenge, but we know it can be done. M-Pesa, Kenya's famous mobile payment service, is now so large that it powers one fifth of the country's economy. Globally, progress may still be slow, but with new "digital wallet" services getting ever better, the number of the "unbanked" is set to plummet.
3.Which leaves us with arguably the biggest but also least-understood problem: the unaddressed. 4billion people around the world don't have an address. However, this is not just a problem in rural areas and the rapidly growing megacities of developing countries. Take the Middle East, where even ultra-modern cities struggle to maintain an address system; with little urban planning, all-too-many buildings simply don't have a proper, easy-to-find address.
Let's be clear: an address is not a "nice-to-have". Without it, you will struggle to get a passport, stake a property claim, become an active consumer, take out a low-interest credit, or run a business. In his book The Mystery of Capital, the Peruvian development economist Hernando de Soto put it this way: "Without an address, you live outside the law." You might as well not exist.
Just a few weeks ago I was in Rio de Janeiro, Brazil, where I visited a favela called Rocinha. Maps of the area will show you 10 to 15 roads. In reality, there are more than 3,000. Yes, it's a tough place, but also full of economic ambition.
Nearly half of the population, for example, are rich enough to own a flat-screen TV. However, economic development in Rocinha was stunted, because the favela was more or less without addresses - until now. By chance, a local co-operative - Carteiro Amigo - that delivers mail to residents, discovered the addressing solution developed by us at what3words.
what3words does what it says on the tin. We have divided the world into 57 trillion squares - each three metres by three metres - and every square has a unique three word identifier, for example type.heat.sketch. It currently works in eight languages, and we are about to add another four.
We came up with the concept, because of problems I encountered in my previous job helping to organise live music events. Too often, music equipment and the musicians themselves simply didn't arrive where they were supposed to. Together with a mathematician friend, I developed the what3words algorithm - and quickly realised that this idea can do so much more than making sure that bands arrive for their gig on time.
The applications are endless: securing property rights, optimising ecommerce logistics, arranging aid deliveries, tracking epidemics like Ebola, tackling natural disasters, and economic empowerment - they all need the boost of a global address system.
That's because the unaddressed have a fundamental problem. "It is almost impossible for individuals to be part of society without a legal identity, and [...] establishing such an identity often depends on having an official address," argues Professor Anna Tibaijuka, a former government minister in Tanzania.
"Urban development, economic growth and the provision of basic services are inextricably linked to the existence of sound address infrastructure."
However, creating a flexible, scalable and country-wide address system is not a trivial job.
It took highly developed countries like Ireland and South Korea many years to develop new address systems, and both are currently struggling to roll theirs out.
In Ghana, there have been at four or five pilot projects to develop the country's first address system, and all have failed so far to deliver a working model. On houses in the capital Accra, you often see four or five different combinations of letters and numbers scrawled on the walls, each an attempt by some organisation or other to identify and address this building.
The simple fact is that in most emerging economies neither the state nor utility companies have the resources to develop a universal address system.
So people have to hack their neighbourhood. A friend of mine knows a bicycle courier who delivers medicines in a South African township, and draws his own maps to keep up with this sprawling and constantly changing conurbation.
It's entrepreneurial, but not scalable.
People need a simple, accurate and unambiguous address system. We could use GPS co-ordinates, of course, but as they require us to remember two sets of 8 to 10 digits and some letters, they are too difficult to use for most people. After all, while they have been available for years, they have never been used outside the professional geographic community.
And that's the beauty of what3words: people find it easy to remember three words; in contrast, just try to memorise your home's GPS co-ordinates. what3words integrates with many mapping solutions; it works on the most basic smartphones, and even offline.
Most importantly, it has already addressed every single spot of the world - whether you need to find a hastily set-up water distribution point in an earthquake zone, pinpoint a new business somewhere on the edges of Kuala Lumpur or sort out the logistics for a music festival in the countryside.
The unaddressed - it's a problem that's not very visible, but it is an enormous challenge. We need to tackle it, if we want to win the fight against global poverty.