Rivers and Google Maps

[bushd25 1]

I was working on a scale accurate map of La Crosse, Wisconsin using the7trumpets' tutorial and I ran into a bit of a problem. The Mississippi River runs smack through the center of the map, but the area immediately surrounding the river is so low there's no really good way to figure out where the river should be. Then I had an idea -- what if I overlaid the elevation map with something else?

First I thought of using the USGS topo map available through the data retrieval system. The problem with this is that it's a huge file, isn't always perfectly aligned, involves more detail than is usable in an SC4 map, and is tedious to trace.

Then it occurred to me to use an online mapping program. I chose Google Maps because it's fairly accurate, it gives more map for the same screen real estate, minor streams and ponds are omitted, shorelines are simplified into playable shapes, and water is displayed in a nice solid blue. The one drawback to using Google Maps is that you have to take a screenshot to get the image (although Yahoo's now like this, too, and I'm guessing Mapquest will be soon), but it's easy enough to copy only the portion you need.

This method is easiest when working with layers. I used The GIMP, and I had a semi-transparent layer to paste the Google maps into, along with a separate file open for pasting, scaling and cropping the screenshots.

After some trial and error, I figured out an easy way to scale the Google map. When Google displays a map, it overlays the scale in the bottom left corner. Given that SC4 maps render at 16 meters per pixel, a bit of algebra leads to a simple formula:
Scale_factor = S / 16L
where S is distance in meters shown by the graphic scale and L is the length in pixels of the scale interval.

So, if the graphic scale is 100 pixels wide and represents 1 kilometer, the scale factor is 1000 / 16(100) or 0.625. Scaling the Google map in this example by a factor of 0.625 would make it match up with the elevation map already created.

Then, all you have to do is copy the water portion and some helpful landmarks into the semi-transparent layer over the elevation map, line it up, repeat for as many segments as it takes to fill in the river/lake/whatever, and you have your river.

Once pasted in, I turned off the elevation layer and made the Google map layer opaque. I then did a color fill of RGB=65 over the blue water and used a round brush to cover labels, boundaries and roads. The magic wand selector sufficed to cut out the river and paste it onto the elevation layer below. Bingo.

I uploaded the La Crosse map to the STEX, but it's not up yet. Any thoughts?

[Kevin 101]

Just so you know, the map is up and it looks great! I don't know much about mapmaking, but looks like your technique worked

[booman443 0]

Hi, I accually live in La Crosse and when I ran across this post I was amazed...What are the chances that someone would make a map of a town of only 50,000? In any case, I would be glad to give you and information or details that you would need to make your map more accurate as I have attempted to do the La Crosse area many times but each time it seems as though I am just not quite close to reality.

 

Josh

[bushd25 1]

Date: 1/31/2006 11:07:25 PM
Author: booman443

Hi, I accually live in La Crosse and when I ran across this post I was amazed...What are the chances that someone would make a map of a town of only 50,000? In any case, I would be glad to give you and information or details that you would need to make your map more accurate as I have attempted to do the La Crosse area many times but each time it seems as though I am just not quite close to reality.

quote>
The big challenge with real-world maps is that people seem to prefer those that have interesting water and terrain features. Doing a map of a place like Des Moines, Chicago or Miami is interesting if you're looking to recreate its look and feel, but it's nice having more to play with in SC4 when you're just building for fun.

The reason I did La Crosse is that I'd done maps of Wausau and Madison, but they were kind of boring terrain-wise, so I was trying to think of another place around here that would give more variety. Anywhere along the Mississippi from Red Wing to Dubuque really fits the bill for that, and I've had a lot of good times in La Crosse, so I chose that.

I know it isn't perfectly accurate in terms of where the river is, but that's why I chose the Google Maps representation -- there really isn't a good way to do swampy river bottomlands in SC4. It's more realistic from a gameplay perspective, IMO, to leave those areas as river.

One thing I have noticed playing the region is that I'm having a bit of trouble laying bridges with the Tunnel and Slope Mod because the land next to the river is so low and I'm making the bridges high enough for ferries (which is the case in reality) -- the approaches get too long when the river is close to one edge of the map. But it's a realistic effect; if you ever drive through Dubuque, the old Highway 20 bridge has an enormous western approach that goes clear over downtown and up the river bluff.