Like it or not, we are indeed becoming a society tethered to our electronics. If anyone doubts that this is the "information age," know that recent surveys estimate that nearly 40 percent of the U.S. population carries a smart phone in their pocket or purse.

And entrepreneurs are pursuing them, building applications so quickly that "there's an app for that!" has already become a cliche.

With more than 200,000 phone apps available for your iPhones and iTouches, and a growing number of apps for Droids, Androids, Blackberries, and other smart phones, no one should be surprised that a few touch on national parks.

Download one of these applications and you'll capture a miniature guidebook in the palm of your hand. Words, pictures, videos, and, in some cases, even links are at your beck and call (as long as your batteries are good, of course, and, in the case of links, you've got a WiFi signal).

Do you need them?

There's no question that a smart phone or iTouch is more convenient than toting a printed guidebook around. And, sadly, guidebook publishers, not quite sure how to compete with the Internet, are not cranking out park guidebooks, or updating them, as regularly as they once did. And yet, you could say the phone apps are abridged versions, for data space limitations can limit the content you'll find in your app.

Speaking of that content, some apps do a better job of indexing content so you don't have to spend time searching the system. Not all are as intuitive as I'd like. Perhaps it's a generational thing, but I've felt at times as if I'm poking around in the dark looking for information or wondering what I haven't discovered. Perhaps app developers could do us all a favor and embed a "user's guide" into their products.

What should you look for in a national park app? Just as there are good guidebooks and not so good guidebooks in terms of content, there are good apps and not so good apps. The good ones are relatively rich in content. I use the term "relatively" because space limitations can at times lead to content limitations (but there are exceptions to this rule of thumb, as I'll note in a separate review of two new apps).

As for that content, there are the basics to cover, of course, information such as trails to hike, overlooks to gaze from, activities to partake in, and wildlife to look for, just to name the four most obvious topics that should be covered.

History naturally is good to have if it's pertinent to the national park in question. While I have yet to see an app on Valley Forge National Historical Park, when that one arrives it better make more than just a passing reference to that war between the upstart colonies and the English. Ditto with geology when the park at hand is Arches or the Grand Canyon.

Photo support is important, too; as they say, a picture is worth 1,000 words, and why try to describe a unique national park setting or structure in 100-200 words and not support that text with an image?

You also want to invest in an app that will be updated somewhat regularly. While much park information -- trails, overlooks, wildlife -- isn't going to change, there are times when sections of parks are closed for construction projects, such as work now under way at Valley Forge around Washington's Headquarters, or those seasonally pesky road projects. Knowing about those things before you reach the park often can be a time-saver, especially if there's a quick way around road projects or if you realize you should cross a particular hike off your itinerary because a bridge is washed out.

You'll know when updates are available because your device of choice will inform you that one is waiting.

Also, you want an app that works with GPS, so you can track your movements in the parks.

Those are the basics. Beyond that come bells and whistles.

Chimani, which recently released its application for Acadia National Park, offers tide charts, sunrise/sunset data, and even shuttle bus schedules, stuff that's nice to have at Acadia, where you might be planning to sea kayak or tide pool, want to know when you should be atop Cadillac Mountain to be among the first in the United States to catch the rays of the Sun, or are wondering when you need to be at the trailhead for a lift back into Bar Harbor.

Nomad, which just released its Great Smoky Mountains National Park app, meanwhile, offers a handy, alphabetical index to help you sort through the content. You can, for example, dive into the "Nature & Science" section, or head over to "Kids & Family." This company also offers two versions of its app, a somewhat basic edition and one that's much more robust.

We take a more in-depth look at these two programs in this review.