How exactly does reach work?

[Casper Gronemann]

Under the rules for Space, Reach & Threatened Area, on www.d20pfsrd.com, two different measures for reach appear. One states that reach is like area-of-effect template, in that you threaten and can attack an area like the radius-template of a spell or other effect. The other states that you simply threaten every square within the feet-indicator of your reach.

In pictures, one gives these rules for reach: http://www.d20pfsrd.com/_/rsrc/1389122892341/images/size-space-3d.png

While the other gives these: http://www.d20pfsrd.com/_/rsrc/1389073071030/images/large-tall.png

What am I missing?

[Beopere]

The Large-tall image is correct. The other image accurately depicts sizes, but, I believe, is mistaken on reach.

Breakdown, medium creatures have a reach of 5 ft.

Large creatures can have natural reach greater than 5 ft, Large tall for examples has a natural reach of 10, whereas large long remains at 5.

A natural reach includes everything inside of it. So if an ogre has reach 10, he can also attack things within 5 feet.

Adding a reach weapon doubles your natural reach, but also EXCLUDES things smaller than it. For example, a medium creature with a reach weapon can reach 10ft, but cannot hit 5 ft. An ogre can reach 15 or 20 feet, but cannot reach 5 or 10. Of course they can unarmed strike or carry a second weapon etc, but I'm speaking for that particular reach weapon.

There's a table somewhere that tells you what size has what natural reach default. Some creatures violate this. For example Dragons are long, but their bite has reach as if they were tall. Large long 5ft reach (10ft with bite).

[digitalpacman]

Those are the same images... the first one isn't with a REACH weapon, it's a TALL large creature vs a LONG large creature. Long large creatures don't have reach, typically.