It is a technical question and can have many different answers to it. Walking and travelling are sometimes different. You can walk to the cross, but you can also use many other means to travel. You can use your vehicle or public transport system to travel. But walking a certain distance cannot be a parameter of being a traveller.
Travelling is reaching a pre-decided destination using so many means of transportation available today. Walking is a physical exercise that can also be used as a means to travel to reach the goal. To be termed as a traveller, it is not important that you need to walk a certain distance. You may be called a walker or runner, as in “Forest Gump”. But was he a traveller? No one thought so. Many were running after him, following him without knowing about his destination or his intentions as to why he was running like this. Once he decides enough is enough and returns to his home, all others also dismantle without knowing what they are doing and why.
Travelling can be termed a hobby of a person. Going to a new place you never visited can be the most incredible urge to travel. You may be a Globe-Trotter to see the world. But it may be a lifetime task if you only walk to complete your mission. There are areas where you have to avail the public transport services, especially when crossing a sea or an ocean. You must have solid ground under your feet if you wish to walk. You cannot walk on water or in the air, and you have to have the means of travelling invented by man to travel on such surfaces.
About our planet Earth:
Scientists discovered that our planet Earth’s equatorial circumference is about 24,901 miles or 40,075 km. But from pole to pole, the meridional circumference is about 24,860 miles or 40,008 km. This difference is because of the shape of the planet. Our planet is flat on its poles. So a walker cannot travel more than this distance even if he decides to cover the whole world in his lifetime, as in “Around the world in 80 days.”
Travelling and walking are two distinctly different things to do. You can walk round and round, reaching nowhere but covering a great distance in terms of covering miles on the road. But this does not make you a traveller. You can be called a walker but not a traveller. Travelling takes you to new places you want to reach, and yes, walking may be one of your means to do so. Currently, people call it hiking. But it is now also Hitch hiking, where you avail the assistance of travellers on their vehicles going the same way you are going, asking for a ride.
The walker who was a traveller:
Meegan covered on foot a distance of 19,019 miles from Tierra Del Fuego to the Northernmost point of Alaska. He took 2,425 days to do so. He started in the year 1977 and finished his walking in the year 1983. It is a record of the longest unbroken walk with the most degrees of latitude ever covered on foot by a man.
There are others in the later years who accomplished globe-trotting on foot, visiting even up to 22 countries. Human capacities have limitations; a man can walk up to 26.2 miles daily with proper training.
So, if you want to walk to have good health, by all means, you can do so. But to become a traveller on foot, you must have perfect health and professional training. And you can cover the entire perimeter of the Earth on foot to be called a traveller. But there is no minimum distance limit decided for the title.
