A great start, but I see something that is catching my eye far more than the repeating textures. Does it take 3 passes to render?

If it does, and you are now asking your screen how the heck I knew that, I'm looking at the horizontal bands across your map.
This can happen if you have really wide glows, shadows or edge fades in operation (which by the look of things you have), and it is caused by the width of each pass.  If the object casting the shadow, or the edge of the polygon with the edge fade on it isn't visible in the current pass width, CC3 can't see the sheet effect, even though the result of it falls within the pass.

You can check the pass width by typing EXPORTSETMPPP on your keyboard and hitting return.  Check the number that shows in the command line.  Unless you have changed it before the default value is 4000000 (4 million).  You can increase it by typing 40000000 (40 million) and hitting enter.  Try rendering the map again with the same settings as before.  Hopefully by increasing the width of the pass this way you will get the whole map in one pass and those horizontal lines will vanish.

I hope these new gum trees look about right. I had trouble deciding what basic colour they should be. I also did some more work on the saguaros. They should be a more realistic shape now.

I'm going to stop worrying about the relative scale. All the tree objects are roughly three sizes - small, normal and large. That's so you can still tell what they are on the map, despite their relative sizes being different in reality.

Yes :)

Just like any other symbol. You right click while you have the symbol on the crosshairs, and click Separate x and y values, then enter different values in the boxes.

I'm only speaking from memory here, but I think you have to go into edit mode to create a poll anyway. It's an integral part of the initial thread-starting comment.

You could always try one and delete it if it goes wrong. That's one of the advantages of the forum - you can delete stuff that goes wrong.

Try a dummy thread, then delete it once you've worked it out.

@jslayton - thank you very much. A very useful pair of images, since they also contained things I knew the size of - vehicles. It is plain to me that what I thought of as tree sized plants are really no larger than a temperate zone shrub. My mother, for instance, has things in her garden she calls 'shrubs' that grow taller than the average Joshua tree. Still a useful map symbol, though, since that whole desert area seems to be covered in nothing but Joshua trees and dry grasses. Thanks also for comments about the saguaro. I had been toying with the idea of adjusting them a little - particularly the really big one. They are a bit on the fat side.

@Quenten - Thanks. I realise the gums are a vast family and vary hugely in size. Not all of them have white bark either! The range you gave is enormous - the largest being twice as tall as the smallest. I think, though, that I am going to have to keep the size variation down to a much smaller range, or they will look raggedy rather than making a reasonable attempt at graceful, in a map where most other types of vegetation varies only by about 10 feet at most between individual trees. The gums look small compared to the palms, but the palms themselves are bigger than the gums. The tallest palms in the world are Columbian wax palms, which can reach 200ft. Again - palms can also be as short as a man when mature, so it's really difficult to know how big to make the different types of trees relative to one another. If it is any comfort the gums are taller than the regular deciduous trees.

@mike robel - Thanks - interesting information. The saguaro can reach 60ft, but the ones I've drawn could probably be a tad smaller than they are. It may well be that once I have shrunk the saguaro and Joshua trees down a bit to more like half the size of all the other trees everything else will look far more reasonable. After all, I don't think anyone is going to need to make a dense forest of saguaro or joshua trees any time soon. They are more likely to just be dotted around to indicate 'desert'.

...

Overall, I think Joe has the right of it in his first paragraph. These are symbols. The fact that all the trees look a bit large beside the mountain is pretty normal in overland fantasy maps. That is down to the need to be able to recognise the different representative types of tree - symbols that say what they are, rather than being totally accurate but otherwise illegible dots in various different shades of green and brown. Meanwhile, the mountains can't be too large, or there would be no room for anything else in the map.

I will play with the relative scaling between the vegetation types a little - make the desert flora a shade smaller, but I won't be able to go too far with it, since the images are already pretty pixelated at the scale they are.

Thanks everyone! ?