Assuming the earths land area was divided up into cells, each of which is the responsibility of one person to monitor, how large an area could each person monitor, and how many people would be needed?

Given that average walking speed is 5 km/h, and suggested limit is 25 km/day, which equates to 5 hours of activity. The suggestion on hand books on human fatigue, and shift work also suggest working for no more than 5 hours between rest periods with a minimum duration of 10 minutes. Also the approximate distance can see is 5 km to the horizon.

So assuming a circular region of 5 km radius, then a person located at the centre can see to the boundary, whilst when at the boundary they can see back to the centre. All assuming have relatively flat land and no obstructions in the line of sight. The perimeter of the circle is 31.4 km, if patrol comprises of walking from centre along radius to the perimeter, around the perimeter and then back along a radius to the centre. Then the two radial legs total 10 km, leaving 15 km for the arc of the perimeter. It would therefore take 2 days to patrol, unless increase daily travel to 41.4 km. Accepting two days for the patrol, then would need 1,896,363 people to monitor the whole planet.

If do not accept the two days, and do not accept increase in total distance travelled, then need to reduce the size of the region: assuming no technological advantage. If do so then the radius decreases to 3.018 km., or diameter of 6.036 km. Which doesn't fit with my preferences for simple multiples of 5 or 10. So rather than only being able to see the centre from the boundary, have so that can see the opposite boundary, and further can see the centre of the adjacent cell from the centre. That puts the diameter of the cell at 5 km, and its circumference at 15.7 km, and the total trip at 20.7 km, requiring a population of 7,585,452.

Of course rugged terrain and obstructions would create a maze which would have to be travelled, and that would further reduce the size of the cell. Whilst the size of the cell can be increased by the use of look out towers, telescopes/binoculars, and the use of a mechanised vehicle. However whilst a vehicle can travel faster, such increase in speed would not be much use except for large open regions. Assuming car travelling at 50 km/h and still limit activity to 5 hours, then maximum travel per day is 250 km. Then the diameter of the cell is increased to 60.4 km, however do not have a view of the perimeter from the centre nor a view of the adjacent cell. Assuming that is acceptable then total population required reduces to 52,045.

It would therefore appear that the planet is occupied by enough humans that they can locate observers across the whole land area, and monitor the environment. For that matter most countries have large enough populations that they can place their own observers across the planet.

It also suggests that a town should be less than 5 km diameter. Messes up my previous concept of an industrial city-state 100 km diameter, divided into towns 10 km diameter, each divided into villages 1 km diameter, into estates 100 m diameter, into personal dwellings 10 m diameter. The city-state having a maximum imposed population of 10 million, and maximum of 2/3rd land taken up by the infrastructure or otherwise no less than 1/3rd for residences. Also assuming a maximum sustainable world population of 10 billion, then 1000 industrial city-states would be needed, taking up approximately 5% of the land area.

At some point in the future all mining operations should be shutdown and all materials held in the city-states. The only activity outside the city-states being agriculture, tourism and environmental monitoring. Most agriculture however would be intensive agriculture within the boundaries of the city-states.

Also given long range aircraft can travel distances of 10,000 km, and typical commercial aircraft can travel 5,000 km, Then aircraft can get from coastline to coastline of most land masses, and from coastline to the central interior. Coastline to coastline is also possible by sea going ship, whilst slower, a sailing ship doesn't require fuel to be transported to the destination at some previous time. Ships are also typically used for transporting fuel not aircraft, the use of aircraft for fuel transportation seems limited. Therefore getting fuel to the interiors requires land transport or pipelines. Ultimately pipelines are wasteful if have small quantities, as the pipe has to be filled with unused fuel. It seems a diesel electric train can travel 1000 km. Therefore the starting point to occupy and hold the land would be a network of railway stations and outposts at 1000 km centres, pushing fuel to airports at 5000 km centres. To this network would then be car fuel stations and general stores at 500 km centres, and then added to this would be human rest and refreshment stations a 5 km centres. Civilisation is where the inn's, hotels and motels are no more than 5 km apart. When the next nearest inn is more than 5 km away, then reached the edge of civilisation, the edge of the occupied zone. {Assuming can walk 25 km each day, then can push this distance to 25 km on condition that there is at least some space where a person can rest, and they carry their own refreshments.}

Using modern GIS, it shouldn't be too difficult to over lay a grid of circular or hexagonal cells on the land areas. To individually triangulate the networks of motels, fuel stations, railway stations, shipping ports, airports, mining towns and farming regions. To then identify the edge of civilisation and the great unexplored wilderness. Once have the triangulation to also compare with the actual roads and railways. Then to create pathways forming a travel plan visiting at least one hotel in each 5 km to 25 km diameter cell, and travelling around the world doing so. The trip should follow the coastline and crisscross through the interior. If all nodes cannot be visited in one year, then have a 5 year up to 10 year plan to visit all nodes. However long the plan is, the world is traversed each and every year: the nodes visited each year just change until all nodes have been visited, then the cycle repeats.

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Revisions:

[13/08/2016] : Original