So here's where we're going to draw a grid. For this example, we'll draw a one-mile grid, with twelve blocks per mile. That means each block is 440 feet. Set JOSM's measurement mode to your desired units of measurement, in this case "Imperial" (feet/miles).
Draw a way along one edge of where the grid will be. Don't worry about any intermediate nodes. That little measurement box at the bottom is useful.
New that we've drawn one edge, it's time to use the parallel way tool.
Make a parallel copy of the way. Pay attention to the measurement box. We're shooting for one mile, which is also 5280 feet. It's okay if you don't get it exactly right — surveyors are subject to error from time to time. Also, the tool seems to snap to whole numbers of feet, which is helpful for us now, but might not always be..
Draw a line connecting the two ways. JOSM will want to make it an extension of one of the existing ways…
… so we zoom in on that point…
… select the node and press P to split the way into two.
Now we use the parallel way tool again. This time we're shooting for a distance of 440 feet, or one block.
Again, using the parallel way, we create the next street. We'll start with the edge street and go 880 feet, or two blocks. We could just do 440 feet each time from one street to the next, but this method is prone to accumulated error. But maybe you're okay with that.
Here we're going four blocks, or 1760 feet. I'm not going to show the creation of every single street, because it's basically just more of the same.
I tend to do streets in four-block (1760 feet) steps, then do the two-block steps (880 feet) between them, then I finally fill in the remaining odd blocks (440 feet).
Now we've got all our north-south streets, but they aren't actually connected to the east-west streets. So let's pick the select too…
… we'll select all the nodes…
… and it doesn't seem to matter whether any ways are also selected for the next step.
Now we activate the Move Node Onto Way command.
As you can see, those east-west streets are now connected to all the north-south streets, and they have all the intermediate nodes they need.
Back to the parallel way tool! 440 feet…
A bit later in the process, finishing up with 440 feet again. As I've said, it doesn't matter much in what order you do these streets, but doing it like this reduces the potential for accumulated error.
It's not obvious at this zoom level, but none of those new east-west streets are connected to the north-south streets. In fact, those north-south streets don't have the necessary intermediate nodes to make the connections, though the east-west streets do. The next step will fix that. But first we need to select all those nodes.
It doesn't really matter if the ways get selected too, except it shows a little more clearly that the north-south streets consist of single segments, skipping all those potential intersection nodes.
So again we use the Move Node Onto Way command. If you're zoomed out too much, this can spectacularly mangle your grid, but the step is easily undone so you can zoom in and try again.
And now we have a completed grid, perfectly orthogonal and completely connected at each intersection. Now all that's left is to add highway=* and name=* tags to all those ways.
Copyright ©2014 David K.