That big blue slice covering 59% of the pie represents Apple’s (AAPL) share of the U.S. smartphone traffic in April as measured by AdMob, the world’s largest purveyor of ads on mobile apps and websites.

By the same measure, Apple also had the lion’s share — 43% — of the mobile Web traffic worldwide.

The point of the “AdMob Mobile Metrics Report” for April 2009, released Wednesday morning, was not to give comfort to Apple’s CEO. Rather it was to measure the large and growing shadow cast on the Internet by smartphones in general.

It cites a Gartner report that smartphones represented 12% of total mobile sales in 2008, and points out that those devices represented 35% of AdMob’s traffic in April — nearly three times their market share.

But Apple’s handheld devices — whose Internet shadow is more than five times their share — ended up dominating most of the report’s charts. Among the highlights:

• 
  Of the 7.5 billion AdMob ads displayed on mobile devices in 160 countries around the world, 2 billion were displayed on iPhones or iPod touches
• The iPhone OS has only 8% of global smartphone market share, but generates 43% of mobile Web requests and 65% of HTML usage
• In the United States, 20% of ad requests come from iPhones, 14.8% from iPod touches (globally, those numbers are 15.1% and 11%, respectively)
• Apple’s share of U.S. ad requests grew 5.6% month over month
• The iPhone’s share grew 3% in April; the iPod touch’s grew 2.6

Those growth figures for Apple contrast with its competitors, most of whom lost share in the same period, including Motorola (MOT), Research in Motion (RIMM), LG, Kyocera (KYO) and Palm (PALM). The exceptions were Samsung, Nokia (NOK) and HTC, which grew marginally. See charts below the fold.

According to its website, AdMob stores and analyzes every ad request, impression and click from more than 7,000 mobile websites and 1,600 applications every day. Its most recent analysis of all that traffic, issued Wednesday, is available here.

See also:

• iPhone now represents 51% of U.S. smartphone traffic — report
• iPod touch use “exploded” Christmas day

Below the fold: AdMob’s Web traffic numbers by manufacturer and model.