Besides file size, what are the downsides to making a large dimension map?

[swiss]

I started mine at 14400 x 10800 pixels. 300 pixels per inch. It's about .5 GB. I'm not sure it needs to be that big, but I figured it's easier to downsize than upsize later on

Also wasn't sure about the ratio. I did 4x3 as that seemed to be a standard one. Anything I should be wary of there?

[Azélor]

Large maps can be very time consuming to create.
In most case, you might be better with a smaller map with less details but that depends what your goal is.
If your a beginner, I really do not recommend working on a very large map.

but I figured it's easier to downsize than upsize later on

You simply can't upsize it without loosing a lot of details, it become blurry.
If you think you might want to upsize it later, you should use a vector based program instead. You can change the scale without losing quality.

I did 4x3 as that seemed to be a standard one.

1X2 is the most commonly used standard for a full world map.
This has a lot to do with the map projection you are using.

If this is not a full world map, then you can use any size ratio you want.
Unless you intend to display the map on a book or something like that, there aren't any specific size standard.

[mat_r]

Multiple things need to be considered here.
Ultimately the most important thing is, what size you want the map to actually be looked at. (and to a lesser degree: from what distance)

If you are going for a 48x36 inch print, then yeah, those 14400x10800 pixels of resolution are exactly right. However the same resolution is (potentially) not optimal for viewing the map on a tablet sized screen, for example. More resolution is not always better. Here is the problem:

While it is true that downsizing is easier than upsizing, downsizing can also lead to problems. First and foremost this is true for all graphical elements that are based on lines. For example: drawings and fonts (paintings/photos not so much) The potential issue with these elements is the following: as you downsize the image, the actual lineweight will decrease, too, and eventually become very fuzzy, noisy or vanish altogether. Fonts that look good on a big scale might look like an utter mess at a very small scale etc. etc.

Long story short, it might work, it might be a catastrophe. It depends on the image. That's also why I mentioned viewing distance in the beginning. Let's say you designed your 48x36" poster for viewing from a 10ft. distance. That means you probably worked with rather heavy lineweight in the first place, so things still look good from a distance. In this case downsizing might just work fine. On the other hand, if you designed the same poster for examining tons of intricate detail from up close, the downsized result might be a total mess.

/edit: let me rephrase that bit about "more resolution not always being better". Usually there's nothing wrong with high resolution. All I really want to say is, if you intend to downsize the result later or if you need it to work on smaller formats, too, design your map accordingly. Make smaller prints/save smaller JPEGs during the process and check if everything looks good. If you run into problems adjust your line weight.

[Falconius]

Most people size their maps according to standardized print sizes A2, A4, A5, etc. at 300dpi. Be aware of course of leaving room for the margins. I'm not sure if professional printing machines can print right up to the edge (or even if they wanted to) but even if they can you want a little bit of margin to protect the picture from edge wear.

If the work is intended only for screen I'd suggest doing it in multiples of screen ratio 16:9 or smaller, 5K (5120x2880) would be an extremely large map. Most people don't want to zoom more than once (or at least I don't) so for a zoomy map I wouldn't actually go above 4K. And of course one should take in consideration that if its viewed in a browser you loose an indeterminate amount of screen space from the edges, so making it 20 pixels smaller on the sides and more on the height might not be a bad idea. Also keep in mind it is easier to scroll up and down than sideways, so tall maps might be more appropriate for computer consumption.

None of this takes into consideration of the projection itself which may also be a factor.

[swiss]

This has a lot to do with the map projection you are using..

I'm not sure what that means; can you elaborate?

[Mouse]

Waldronate gave me a link to a lovely page that explains all about map projections here.

Most fantasy maps don't really have a projection. They just... 'are'... if you see what I mean. Don't worry too much about projection unless you are aiming to make a map of an entire world all in one go, like Kacey is right now.

Most fantasy maps are regional (a single country or province, maybe a small to medium continent), city or dungeon areas. Projection is much less important the smaller you get, in terms of the area covered.

[swiss]

Is the concept of projection entirely to do with the shape of the earth? In other words, if the world was flat, is it fair to say projection would not be a thing? Just trying to wrap my head around the concept

[kacey]

I've found just as many issues with scaling down as I have scaling up, you tend to get blurry spots either way or you end up with text and line weight that is way off so it's best to size it according to it's use. I like to print most things just to have a physical copy of my work so I always make my file the size I want to print keeping in mind the margins that will be along the edges. I've tried printing borderless but it always tend to cut off one way or another by a mm or so in just the wrong spot.

[Falconius]

Is the concept of projection entirely to do with the shape of the earth? In other words, if the world was flat, is it fair to say projection would not be a thing? Just trying to wrap my head around the concept

Yup. If the earth was flat it would not be an issue. It's all about how to represent an accurate depiction of a sphere(oid), or a portion thereof, on a flat plane.

[Mouse]

You are correct. If the world was 2D there wouldn't be any need to distort it to be able to map it in 2D.

Imagine that you have an orange in your hand, and that you have drawn the outlines of the Earth's continents on its skin. A projection is a bit like working out where to make the cut as you peel the orange, and then how to stretch, then press down the entire skin so that it is as flat as you can make it on a flat surface, while attempting to preserve the pattern and shape of the continents you drew on it before you peeled the thing.

EDIT: ninjad by Falconius Drat this slow connection! LOL!