Author and broadcaster Simon Reeve explains what possessed him to take a spherical view of the world, and how his unique blend of travel and current affairs allows him to examine a wide range of social and political issues.
The countries along the equator are among the most troubled
So why the equator? What's the point?
During the past year more than a few friends and colleagues have asked me why I was starting a long journey around the warm waistband of the planet.
For most of us the equator is little more than an imaginary line running 25,000 miles around the globe.
But the equator is actually a unique region with a distinct identity.
Following zero degrees took us across ancient rainforest, paradise islands, and through a gorgeous region with the greatest concentration of natural biodiversity in the world.
Yet, equatorial countries are also among the most troubled on earth and have perhaps the greatest concentration of human suffering.
Visiting the Democratic Republic of Congo took us to the country experiencing the most violent conflict on the planet since the World War II.
And following the line to Colombia took us through the worst humanitarian crisis in the Western Hemisphere.
Sundays on BBC TWO at 9pm
Africa: 27 August
Asia: 3 September
Latin America: 10 September
I would like to have visited all of the countries on the equator but we were barred from several parts of Indonesia by the government there.
We were unable to land in Congo-Brazzaville because an outbreak of the deadly Ebola virus close to the equator made villages a little too unhealthy for visitors.
And as if Ebola wasn't bad enough, the World Health Organisation warned us locals were blaming foreigners for the outbreak and we had a good chance of being killed if we landed.
Much to my disappointment, we were also unable to travel across Somalia. The endless rumbling conflict in that tragic, forgotten land has worsened since I visited the violent Somali capital Mogadishu 18 months ago.
Without a BBC armoured car it would have been too risky for us to attempt to travel across what is rapidly becoming a war zone.
Travelling along the rest of the equator still posed unique challenges.
Habitat destruction in Borneo kills at least 2,000 orangutans each year
The main problem was that nothing went to plan.
Whether it was drivers abandoning us deep in the rainforest, or me developing a temperature of nearly 40C and vomiting blood, there were plenty of days when things went spectacularly wrong (and that was just the start of the first trip).
Because we didn't have bottomless pots of money to spend on private jets or helicopters, we also had to be careful about our route.
Although we wanted to stick closely to the imaginary line, some areas of the equator are fantastically hard to reach and leave, and we couldn't risk getting stuck in a single location for a month when we had an entire planet to circle.
I was worried we would have to be constantly racing along to make it all the way round in less than a decade.
Because the equator is just so long, we had to find a balance between what we wanted to film, and what was physically possible.
By making short leaps along the line, we were able to spend a healthy period of time in each country.
We weren't in any one place long enough to put down roots, marry locals or open a pub, but we did get a good sense of the lives being lived and the challenges facing people, animals and the planet in this unique region of our world.