a lunatic. You’re texting each other or talking distractedly on the phone as you try to locate each other visually. It’s painful.

Assuming one of you has an iPhone, you should try using Marco.

It’s a free iPhone app that lets you share your exact location with a friend. Marco makes it painless to meet up in a crowded place, because it provides real-time updates about where Person A and Person B are by plotting both of you on a map you can both see. The map updates as you move.

The best part may be that you can share your location with any phone that has a browser, so it still works if your friend doesn’t have an iPhone.

The free app is available in the App Store (if you’re searching from your iPhone, you want “Marco friend locator” — just searching for “Marco” returns Instapaper creator Marco Arment as the top result). Open it up and you’ll see a map centered on your current location. Tap the big green “Find Your Friend” button and enter anyone from your address book. Marco sends your friend an SMS with a web link. When they click on the link inside the SMS, they see a map of where you are, and they’re invited to share their location.

Here’s the cool part — the receiving end works through the browser, so the other person doesn’t need any apps, and it works across mobile platforms.

When your friend opens the web link, Marco uses the Geolocation API through the browser to grab their location and update the web service. Within Marco, you’ll see a “Polo” update (clever!) when your friend pops up on the map. As you both move around, the maps stay in sync. You can both watch your locations change as you walk towards each other: You see your friend moving in the Marco app, and your friend sees you moving on the web page. Marco can also spit out directions if you’re in unfamiliar territory.

I tested this app this past weekend at the Hardly Strictly Bluegrass Festival, a free concert in San Francisco’s Golden Gate Park with tens of thousands of attendees. I sent notifications to a few friends — only one of whom had an iPhone — and they were all able to find me in the massive crowd. When one friend walked up, the woman next to me was standing, waving her arm over her head and talking to her friend on her phone: “Look behind you — no, BEHIND you!” We felt like we were in the future, and she was stuck in the past.

I can also see this being an excellent tool for something like South By Southwest, where you and your friend are trying to connect in a strange city where neither of you are sure exactly where you are.

The receiving end of the service works on any smartphone with a WebKit browser that supports HTML5 geolocation: iPhones, Android phones and newer BlackBerry phones. Location can still be pretty spotty on handsets, especially in urban areas or indoors. But you can drag your locator pin on the map — either within Marco or on the web page — to refine your location if you have to.

If your friend doesn’t have a browser that supports geolocation, they just see a static web page that shows a map with your pin on it. Instead of receiving a “Polo” notification, you get a message telling you that your friend can’t share his location, but that he now knows where you are.

But when both of you can see each other, it’s much better than something like Foursquare, Gowalla or Facebook Places for meeting up. Most GPS units are accurate enough to place you within a few meters, so it’s better than just saying “I’m at Gordon Biersch”. You can actually show somebody that you’re seated in a corner on the back patio at Gordon Biersch. You can also see when your friend is about to arrive, so you know when to start looking around you.

There’s no shortage of location sharing apps for mobiles — it’s one of the things that smartphones just seem made for. Foursquare and Gowalla have made a game of it. Google Latitude and Loopt also let you share your location. Glympse does real-time updates, but it only tracks one person. EchoEcho and HeyWAY are other apps for sharing locations between two people, but unlike Marco, they require you to both have the app installed.

Marco is both more secure and more refined than those apps. It’s not a game, it’s a utility. There are no badges or restaurant tips. There’s no social network integration. It’s just a private share between two people, and each share session only lasts 30 minutes. Also, the two-way real-time updates are a key standout feature. You can both watch each other move on the map whether the other person has the app or not.

Marco was built by the Brooklyn company Uncommon Projects. Co-founder Tarikh Korula tells me they’ve been doing hardware and software development for about five years on a for-hire basis, and they’ve just recently decided to branch out and create some apps they can call their own. They first got started thinking seriously about location when they worked on the Purple Pedals project for Yahoo, which distributed photo-snapping, geotagging bikes to different cities around the world.

Uncommon’s first app was BikeNic, a location-aware trip computer for cyclists. Marco was released last week. Go find it.

See also:

• Roundup: Location-Aware Smartphones
• Vail’s EpicMix App Brings Location Tracking, Social Networking to Ski Slopes
• Google Latitude Makes It Easy To Stalk Friends

Authors: Michael Calore

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