Pixelmator does its users a enormous disservice by conflating DPI -- a printer measurement that has virtually no use to anyone except printer engineers -- and PPI. Promulgating ignorance is inherently wrong.
They are very much not the same. A dot is not a pixel. Please note that many of the explanations turned up in that Google search themselves contain addition errors.
Nevertheless, read up on the difference, and then re-read my initial response.
Keep in mind that pixels contain no information about size, and that image-format files contain no useful information about size. Size of an image-format file is determined at the time of rendering the file. When rendered to a computer screen, the size is set by the OS. It can be controlled by the user, who typically does it once per display device, indirectly, and forgets about it.
When rendering images on paper (a/k/a "printing"), the size is set by the user. Until the size is set by the user, there can be no PPI because there are no inches. Importantly, you _are not_ printing fewer pixels or data ("I'm loosing pixels and data as I increase the printing size") when you print larger. You are spreading the same amount of information, and the same number of pixels, over a larger area. The information density decreases, and the resolution of the print decreases, but the number of pixels, and the amount of information they contain, stays the same. Resolution is a measurement of information density: information per unit area. You need to know the number of information units (pixels) and the area in which they will be rendered (inches, for example), in order to know the resolution of a print. Weirdly, perhaps, your image-format file actually has no resolution. The term cannot have meaning in that context. ("Megapixel" is a measurement of the amount of information, not its density.)
(NB: "Aperture", not "Aperature")