Meet Me in the Middle

February 16, 2005 12:04 PM

Is there a map program or website that selects a midpoint between 2 or more locations? I often need to meet people around town (LA) and am in frequently need to pick a central meeting place between 2-4 people with offices over wide distances. Any suggestions?
posted by Carsey to computers & internet (11 comments total)

Well, this isn't exactly a fix, but it should work pretty well: use Google Maps to plot directions between two addresses, then visually scan the area to find the midway point. You can jump directly to a "directions" page by using the following format:

http://maps.google.com/maps?q=from start address to end address use spaces

So, for example, here's directions from my office at the DA to my 5th Ave. penthouse in NYC. Just kidding. :)

You don't have to enter "%20" for spaces, either. Just type the address using natural english (yay, Google!).
posted by Civil_Disobedient at 12:47 PM on February 16, 2005

(Isn't it the browser that's doing the space -> %20 conversion, before it sends off the request? Not to take anything away from the Yay, Google!)
posted by lpqboy at 2:12 PM on February 16, 2005

In LA, I wouldn't go off of equi-distance, I would go off of equal travel time. Also, consider somewhere freeway close and in a location you would want to meet at. If you give me a rough run down on where people are located and what you want to do when you meet up, I can give you a few LA suggestions of meeting spots.
posted by jonah at 3:22 PM on February 16, 2005

Go to http://www.streetmap.co.uk/. Search for the two places of interest and note the x and y values in the URLs.

Create an Excel spreadsheet.

Enter "map" in cell B2.

Enter the coordinate of the first place in cells D6 and E6.

Enter the coordinate of the second place in cells D7 and E7.

Paste the following expression in cell C6:

=HYPERLINK(CONCATENATE("http://www.streetmap.co.uk/new", $B$2, ".srf?x=", $D6, "&y=", $E6, "&z=2"))

Copy it to C7 and C8 (select C6 and drag the tiny square at the corner, you can't just paste the same expression in three times - Excel copy is magic).

This takes an x coordinate in column D and a y coordinate in column E and the word "map" or "print" in cell B2. It displays as a clickable link (click and hold to select the cell instead of following the link).

Paste the following expression in cell D8:

=INT(SUM(D6:D7)/2)

Copy it to E8.

Cells D8, E8 now contain the coordinates of the place midway between the other two places and C8 is its URL.

I name the locations in column B to make it easier to re-use rows later.

You can easily extend the idea to average over more than two places.

I use this for picking places in London to meet friends for drinks and for plotting cycle routes. Let me know if it works for you.
posted by denishowe at 4:04 PM on February 16, 2005

Unfortunately, denishowe, your simple equation (dx2-dx1/2) does not take into account the curvature of the Earth. What you've done is give the midpoint of two locations on a plane, but the Earth is a (quasi) spere, which means that point will be buried somewhere under the Earth.

I could give you a somewhat better equation for the midpoint on a sphere, but it would require substantially more mathematical efforts on the part of the Original Poster, so I won't bother.

:)
posted by Civil_Disobedient at 4:13 PM on February 16, 2005

http://www.streetmap.co.uk/

That site seems to be UK-only.
posted by goethean at 5:25 PM on February 16, 2005

Anyone know of a site where you don't have to create an Excel spreadsheet?
posted by MLIS at 9:15 PM on February 16, 2005

That's the best answer!? I thought that was supposed to be funny!
posted by Civil_Disobedient at 9:59 PM on February 16, 2005

Dear Civil_Disobedient, you have a very interesting point about the curvature of the Earth. Interesting, but totally irrelevant. For that to be an issue, we would have to be working with three-dimensional coordinates that span the whole volume of the planet, whereas the (x, y) coordinates that Streetmap uses are related to latitude and longitude - a 2D system that coves only the surface.

One day I will turn my spreadsheet into a web app.
posted by denishowe at 12:14 AM on February 17, 2005

Denis, I'm sorry to have to be the one to tell you this, but the shortest distance between two points on a sphere is an arc, not a line. You cannot use simple 2D Cartesian coordinates to determine "halfway" by dividing the difference between longitudes (and then latitudes) by two.

The "basic" equation for determining just the distance between two points on a sphere is:


You can read more about how wrong you are here.
posted by Civil_Disobedient at 5:23 AM on February 17, 2005

OK, OK, so there might be some error due to the fact that a given difference in latitude is less significant the further you get from the equator. That would make my mid-points slightly too far North but none of my friends live or work at the North Pole and Streetmap doesn't cover it anyway so the worst that could happen is we end up in the wrong pub.

I still reckon that, allowing for undefined latitude at the poles, the mean latitiude and longitude is still a pretty good mid-point (or mid-line in the case where someone from the North Pole wants to meet someone from the South Pole for a drink somewhere on the equator).
posted by denishowe at 4:34 PM on February 17, 2005