If you believe in investing "in your own backyard," as some advisers suggest, then Georgia is a good backyard to explore.

The publicly traded companies headquartered in the state are spread widely over industry groups and subgroups. Individual companies range in size from less than $10 million in market value to $140 billion or more.

Indeed, a dozen corporations headquartered in Georgia were big enough to find a place on this year's Fortune 500 list, a benchmark of business size and success. Fortune ranks companies by annual revenue, with the latest list based on 2007 results.

Among them are home-improvement retailer Home Depot at Georgia's highest rank (22nd). UPS, a global package-delivery company, was 46th, and possibly the best-known corporate moniker on the globe, beverage giant Coca-Cola, was in 83rd place.

But "big" does not accurately describe the universe of publicly traded companies headquartered in Georgia. Most are "midcaps" or "small caps." That's Wall Street jargon for " mid- or smaller-capitalized" companies, or size based on market value —- share price times the number of shares outstanding.

There is no official definition of "small," but some analysts put it at anything less than $700 million; others put the cutoff at $500 million.

Small vs. large

In Georgia, two-thirds of the publicly traded companies have market caps of under $500 million. But among them are well-known names, such as Georgia Gulf, CryoLife, Haverty Furniture, Oxford Industries and Spectrum Brands.

Not to be overlooked, roughly a third of Georgia's public companies have market caps of less than $100 million, which some analysts regard as "microcap."

For investors, small vs. large is a point to take seriously. According to money managers, the stocks of smaller companies have historically outperformed big-cap stocks in periods of economic expansion. That has certainly been true of most years since the last Wall Street bear market that ended in 2002.

But the tables turned in 2007, when small-cap stocks took a hit in total return because of the impact of the mortgage and credit crisis on banks and real estate-related companies.

The damage to Georgia's "backyard" was mitigated, however, by another characteristic of the state's public sector: As a group, the companies are highly diverse. No single industry dominates the state or its public companies, which economists cite as a major reason for Georgia's better-than-average growth over the years.

About 22 percent of the public companies in Georgia are banks or otherwise engaged in a financial service. By far the largest number in this sector are local, or community, banks scattered throughout the state. The two largest are regional financial institutions: SunTrust Banks in Atlanta and Synovus Financial in Columbus, both in the Fortune 500 and always in the Georgia 100.

If insurance is included under the finance heading, the list would include companies such as Aflac, Atlantic American and Crawford & Co., the latter being the world's largest independent insurance adjuster.

The broad consumer market is served by about 22 percent of the publicly traded firms —- companies that make products or provide consumer services. Companies that supply services or products chiefly to other businesses account for an additional 19 percent of the total.

About 14 percent of the companies are in technology and an additional 9 percent in health care, while a surprising 14 percent are industrials, or manufacturers, of one kind or another.

A big percentage of Georgia's public companies operate globally, through foreign operations, trade or services. Coca-Cola, Delta Air Lines and UPS are among the giants in this sector, but many smaller companies also make money overseas.

Invesco now official

One global company, Invesco Ltd., a leading investment advisory firm with a $10.2 billion market value, has long been an Atlanta business. But it did not officially become Atlanta-based until 2007, when it relocated its headquarters from London.

That also made it eligible for the first time to be included in the Georgia 100, where it is No. 15.

Another example of global diversity is IntercontinentalExchange, a $9.4 billion market-cap Atlanta company that operates a worldwide Internet commodity exchange market, with major operations in New York and London.

It's not surprising that Georgia is home to a relatively large number of public companies, given the state's central place in the Sun Belt.

Georgia was a recipient of the historic migration of people, business and industry from North to South in the post-World War II era, known as the Sun Belt phenomenon. This migration gained momentum in the 1960s and accelerated in subsequent decades.

Georgia is by no means the only state that experienced this growth, of course. While it is home to 12 Fortune 500 companies on the latest list, Florida and North Carolina have 14 each.

That's a reflection of how much the Southeast's growth has evened out over time, thanks to more competitive industrial and business development programs —- and state-sponsored financial incentives —- in all the states in the region.

Go to ajc.com/georgia-100 for these online exclusives:

> Compare and re-sort how the companies rank in five separate financial benchmarks.

> Individual company profiles, including clickable links to each company's Web site.

> Clickable ticker symbols for updated market data and charts you can customize.