The Energy Information Administration, or EIA, announced earlier this week that there were only 367 miles of natural gas pipelines built across the U.S. last year. As demand for natural gas climbs, keeping up our infrastructure is incredibly important. Today I'll take a closer look at what investors really need to pay attention to when it comes to building out our pipeline network.

A brief construction history
Over the past 15 years, we've built a considerable amount of natural gas pipeline. Construction really dropped off last year, however, after a massive build out in 2008 and 2009:

Source: EIA

In 2011, we spent nearly $10 billion adding just shy of 2,500 miles of new pipeline. With the exception of six projects smaller than 100 miles each, that construction occurred outside of the Northeast region.

Though we built less than 400 miles of pipeline in 2012, most of that construction was in the Northeast, a region that is particularly wanting for infrastructure as production booms in the Marcellus Shale.

The more important number
This year, the EIA expects operators to bring on line more than 1,000 miles of natural gas pipeline projects. More importantly, capacity additions should reach 15 billion cubic feet per day, after failing to crack 5 bcfd in 2012.

It is important to distinguish between capacity and miles when we attempt to reconcile this construction growth. Capacity can be added by increasing pressure at compressor stations, or more obviously, by using bigger pipes. Taking a look at our next two charts really hammers home this point.

First we have the number of miles constructed in the Northeast from 1997 to proposed miles in 2015:

Source: EIA

Far and away the biggest growth year was 1999. Now let's look at capacity additions over the same period:

Source: EIA

Right away the difference is striking. There is very little correspondence between miles constructed and capacity added. The easiest comparison to make is between 2012 and 2013. Construction miles in the Northeast are expected to increase slightly this year, but capacity will jump through the roof.

Why this matters
Our world is full of numbers, but not all of them matter. In the pipeline game, capacity and connections to valuable markets are much more important than mileage.

Take for example, Enterprise Products Partners' (NYSE:EPD) ATEX Express pipeline. It's a long line that will travel from the Marcellus Shale down to the Gulf Coast, and it will certainly increase the company's overall mileage statistics, but that doesn't matter at all. What matters is that it will add 190,000 barrels per day of capacity to a region that desperately needs it. Chesapeake Energy (NYSE:CHK) has gone on record saying that it will not increase its liquids production in the Marcellus until this pipe comes on line. Range Resources (NYSE:RRC) is also counting on the project to deliver production to the Gulf.

Foolish takeaway
Whether or not you are a midstream investor, there is a good chance that pipelines will affect your oil and gas investments. Knowing in advance which information matters most with these new projects can save time when you're researching new opportunities. Enterprise Products Partners is one of those opportunities right now.