Map/street direction system

ph3n0m

Just wondering what would the best way to go about creating a street locator/direction system

For example, some types in their current location and enters/selects their destination - how would you go about developing the relationship for something like that.

I am in a bind as I am thinking would you enter each street as its own row, and that any adjoining streets would be associated with it

What type of queries would I be looking at running

Apologies if this is in the wrong forum

greenie2600

Are you talking about building your own navigation system, like Mapquest or Google Maps?

I'm no math expert, so take this with a grain of salt, but I always figured that required graph theory. I think you'd quickly tear your hair out if you tried to implement this using simple SQL tables. Anyway, compiling a complete database of road map data, and keeping it current and accurate, would be a Herculean task.

More about graph theory in this context:

http://en.wikipedia.org/wiki/Shortest_path_problem

If you've got tons of money to throw around, you can sign up with Mapquest's Site Advantage web service, which allows you to integrate Mapquest maps into your site. This is what most major companies do, rather than creating their own home-brew mapping software. Google Maps probably has a similar service.

Or you can just provide a link to Mapquest, with the start and destination addresses encoded in the URL. You'd have to look at a real Mapquest link to figure out exactly what variables to include, and how, but it shouldn't be too difficult.

ph3n0m

No, it wouldnt be a navigation system like Mapquest or Google it would be more of a street directory with directions

A better example might be

User A enters a street name they are on and they want to get to another street

The query/database would return

Start Street
Goto street a, then street b and the street c (destination)

Does that make what I am trying to do any clearer?

An even better example would be something like the oracle of bacon

greenie2600

"A street directory with directions" is exactly what Mapquest is 🙂

If you look on the Oracle of Bacon's "How Does It Work?" page, you'll see that they are, in fact, using a shortest-path algorithm - i.e., graph theory.

Because I was curious (and bored), I started deciphering the Mapquest link I posted above, to figure out what the different variables mean. Here's what I've come up with so far.

Var	Meaning
do	? (e.g., "nw")
2n	Destination county (or "DISTRICT OF COLUMBIA", if in DC)
1y	Starting country (e.g., "US")
r	? (e.g., "f")
1z	Starting ZIP+4
2a	Destination address
mo	? (e.g., "ma")
1si	? (e.g., "navt")
2s	Destination state as two-letter code (e.g., "PA")
2c	Destination city
1rc	? (e.g., "L1AAA")
1da	?
2si	? (e.g., "navt")
2da	?
2rc	? (e.g, "L1AAA")
1n	Starting county (or "DISTRICT OF COLUMBIA", if in DC)
cl	language? (e.g., "EN")
2v	? (e.g., "ADDRESS")
did	? (e.g., 1158334461)
1gi	? (e.g., 0)
qq	? (giant hash)
2gi	? (e.g., 0)
1a	Starting address
2y	Destination country (e.g., "US")
un	? (e.g., "m")
2z	Destination ZIP+4
1s	Starting state as two-letter code (e.g., "DC")
1c	Starting city
go	? (e.g., "1")
rsres	? (e.g., "1")
1v	? (e.g., "ADDRESS")
ct	? (e.g., "NA")
1l	?
1g	?
2l	?
2g	?

ph3n0m

but surely it would be easier if the searching was limited to one particular city?

and to what you posted above, I say thank you and eek!!! what can of worms have I opened 🙂

greenie2600

Aha! I've found the answer to your problem.

In addition to their (very expensive) Site Advantage service, Mapquest offers a free service called OpenAPI, based on Javascript. I don't know exactly how it works, but I'm sure all the documentation is available on their site.

This would be about a million times easier than compiling your own database and writing your own implementation of a shortest-path algorithm in PHP. Why reproduce all that effort when it's already been done for you?

lucasrd

Google also makes their API available...i've implemented it and it's pretty sweet

ph3n0m

excellent - but I may be back - this looks like it might just apply for the USA, since I am based in Ireland, I may have to do it from scratch

greenie2600

Even if your engine were limited to one city, consider the following:

Let's assume that you can create a database that represents the street network in your city (though that's not without its own complications, as we'll see below). Now, how are you going to determine the shortest path between two points? Sure, you can query against the database and determine what roads intersect with the one you're on, but how will you know which one to take to get you closer to your destination?
What about one-way streets? How would your engine know to avoid telling people to turn the wrong way down a one-way street?
What about when a U-turn is necessary? Your map database would have to include nodes for every possible U-turn, roundabout, highway exit, and so forth. (In some cases, it would have to include multiple nodes, since traffic flows in more than one direction on some roads, and the same actions are not always possible from both sides of the road.)
How would you account for different speed limits? Sometimes the shortest physical route might be along 25mph back roads, but the fastest route might be along 65mph highways. (In graph theory, this is solved by giving different "weights" to different edges on the graph.)
Are you absolutely certain that no one would ever want to enter addresses outside of your city?

...and so on.

Graph theory is the way to go. If you're bound and determined to build your own engine, better sign up for some advanced math courses.

greenie2600

ph3n0m, I'm pretty sure Google Maps covers most of the globe. Mapquest probably does too. If not, I'm sure someone has already built another site for your area.

greenie2600

ph3n0m, are you in Irish Ireland, or British Ireland?

It looks like Mapquest Europe covers the UK, but not Ireland proper.

However, Google Maps does cover Ireland. Here's their API.