Area Mapping On Foot

[Jinumon]

Hey all,

Coupled with my discussion of overland speculative trade a few weeks (months?) ago, I've been brainstorming a system for running "hexcrawls" in GURPS.

First of all, huge shout out to Bill Stoddard and Sean Punch for their previous advice and work on DF16 - Wilderness Adventures, respectively. They've been an immense help! On to the actual topic.

From DF16 - Wilderness Adventures, p. 27: "Conquerors and delvers prize area maps. Creating these on foot means zigzagging across a region for longer than is fun for most players."

My question here is, assuming you did have players interested in this, especially as it relates to long-running campaigns, how long would it take?

I should note that I realize the answer to this question is infinitely variable depending on the specifics of terrain; my primary goal here is coming up with something that is reasonable, gameable, and that is preferably more grounded than "as long as you want it to take." What follows is some of my own musings on the topic. I am not an expert on this topic so consider this sentence as one big qualifier for what follows. Feedback and advice is welcome and encouraged.

The smallest scale for area maps seems to be about 1:5,000, wherein one inch on a map corresponds to 5,000 inches, or about 420 feet. Assuming we want a map that is accurate enough to distinguish, say, individual units in a tenement building, we'll probably want it accurate to around 10 feet. That's the modern equivalent of 42 dpi, or about 1,800 data points per square inch.

Jane Cartographer has Cartography-12 and Observation-12. She stands between 5 and 6 feet tall and can see about 3 miles on "flat" ground before the horizon makes further observation impossible. As she walks, she observes a swath of land to her left and right and sketches on a hardback she carries with her.

Jane is unhurried and unthreatened (+4), and while the terrain isn't as obvious as an oncoming car (+10, p. B358), it is stationary and in plain sight (+8). Desiring a map accurate to about 10 feet, she only takes note of the terrain in 3-yard patches (SM+1). Assuming she takes no penalty for darkness or weather, her effective skill is 25.

Jane wants her map to be as accurate as possible. Considering a roll of 17+ is always a failure, she can take up to a -9 and still have an effective skill of 16. The distance at which Jane suffers a -9 penalty on Vision rolls is 100 yards, meaning she can map a swath of land 200 yards wide as she travels. For every mile Jane walks she maps an area of equal to ~0.11 square miles (600/5,280). Assuming she occasionally backtracks or crosses her own previous path, let's say 0.1 square miles.

Conclusion: the base rate at which one can map an area of the Plains terrain type, in square miles, is equal to (linear miles traveled/10).

I really hope I'm not totally off-base with this. Please let me know what ya'll think. Ya'll are the best!

Jinumon

[mlangsdorf]

The normal bonus for "in plain sight" is +10, so Jane can accurately map things within 200 yards, making for a 400 yard observation radius. That would double her mapping speed. Everything else looks good.

Though extreme terrain is going to slow her mapping. If she's going through thick woods that limit her line of sight to 50 yards, her movement speed is slowed but her observation radius is cut down a lot.

[Jinumon]

Originally Posted by mlangsdorf

The normal bonus for "in plain sight" is +10, so Jane can accurately map things within 200 yards, making for a 400 yard observation radius. That would double her mapping speed. Everything else looks good.

Though extreme terrain is going to slow her mapping. If she's going through thick woods that limit her line of sight to 50 yards, her movement speed is slowed but her observation radius is cut down a lot.

I was trying to be conservative, considering the example is "a car coming toward you," but if others agree that would double the base mapping rate.

Assuming my logic is sound I'll just need to figure out some solid baselines for sight lines in various terrains and should be able to expand from there.

Jinumon

[johndallman]

Originally Posted by Jinumon

The smallest scale for area maps seems to be about 1:5,000, wherein one inch on a map corresponds to 5,000 inches, or about 420 feet. Assuming we want a map that is accurate enough to distinguish, say, individual units in a tenement building, we'll probably want it accurate to around 10 feet. That's the modern equivalent of 42 dpi, or about 1,800 data points per square inch.

I think maps with that kind of data density are strictly a modern thing. An area map that's hand-drawn would not attempt to be that detailed: it might show the outlines of a village or town, but there would be a separate map on a larger scale to show buildings with some accuracy.

[Polydamas]

Low-tech surveying is a lot of work with chains and rods and a groma or dioptra interspersed with arithmetic and geometry. If its by eye, its sketching not surveying. A spy or military engineer will be expected to know both. Stories about the British surveys of India and Central Asia in the 19th century are easy to find in English and good models for adventure stories. A bit of digging should turn up how fast survey teams work and how long it took to say sketch a fort that the John Company might have to take one day.

Originally Posted by johndallman

I think maps with that kind of data density are strictly a modern thing. An area map that's hand-drawn would not attempt to be that detailed: it might show the outlines of a village or town, but there would be a separate map on a larger scale to show buildings with some accuracy.

The Forma Urbis Romae looks a lot like fire-insurance maps from the 19th century. Even in the 19th century, nobody tried such maps outside urban centers.

[Polydamas]

The full survey will require a team of labourers to trim and fell trees, build platforms for the surveyor on steep slopes, and so on (and then cooks, laundresses, muletenders, etc. for the labourers). They often get in trouble with locals in remote areas, and local powerbrokers are usually unhappy with the idea that outside authorities will know a lot about them a few years from now.

"Something went wrong with the survey of Upper Ruritania" can be a good adventure hook, as can be "travel to the lands of the Burnt Umber Elves and record all the distances and sketches you can without being defenestrated and fed to the hawksloths." In Dungeon Fantasy, possibly "get this team of surveyors close enough to the peak of Mt. Gloom to measure its height and survey the surrounding country without being eaten by basilisks or sacrificed by the storm cult; the empress' favourite painter wants the proportions in his next landscape to be accurate."

[Anthony]

In a setting with access to GURPS Magic, a number of tools are available that would be extremely useful to surveyors, mostly in the Information school -- for example, Tell Position, Wizard Eye, and Remember Path.

[ehrbar]

Originally Posted by Anthony

In a setting with access to GURPS Magic, a number of tools are available that would be extremely useful to surveyors, mostly in the Information school -- for example, Tell Position, Wizard Eye, and Remember Path.

Or, over in the Making and Breaking college on p.118, Mapmaker.