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The Galaxy Nexus is 1280x720, and the Nexus 7 tablet is 1280x800.

I realize that the tablet is physically larger, but it's screen resolution, not display size, that determines screen real-estate.

Why is it that the Nexus 7 appears to be able to show so much more content on-screen?

EDIT - My question isn't "why was it designed this way". My question is more "how is it that it is able to show more on the screen"? PPI doesn't explain this.

Is it just a matter of the scaling?

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I should have asked "how" is it able to do so. When I said why, I did not mean "why did they design it this way", I meant, "why is this TECHNICALLY possible"? –  zacharyalexstern Jun 29 '12 at 21:23
    
Why is it possible? Seriously? You make things smaller. –  Richard Borcsik Jun 29 '12 at 21:35
    
Also, if you look in the build.prop of that ROM (if you have the ROM dump), there's a line in there ro.sf.lcd_density=xxx that dictates the screen density. The higher the value, the more can fit on screen, likewise the reverse, less can fit on screen. –  t0mm13b Jun 29 '12 at 21:37
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@zacharyalexstern: asking how it's done is development question, and is off topic here. Try StackOverflow. –  Lie Ryan Jun 30 '12 at 3:17

4 Answers 4

up vote 39 down vote accepted

To understand why Nexus 7 can show more content than the Galaxy Nexus, I'll first explain two concepts: screen density and density-independent-pixel.

But before we go into technical details, it may be worth to clarify the design goals of using density-independent-pixels. The goal is to define a UI that is similar in dimension across devices, regardless of the screen size. So in this case the appearance of the menus is the same in the Galaxy Nexus and the tablet (side by side should look very similar), but, as one has a bigger screen, more content can be shown. The designer selects an appearance that looks good for a certain size (a 160 dpi screen is the base) and this is "simulated" in this case in devices with higher dpi.

Screen Density

Commonly referred to as dpi (dots per inch). Android groups all actual screen densities into four generalized densities: low (120), medium (160), high (240), and extra high (320). A device such as Galaxy Nexus has "extra high" screen density (more specifically, the dpi value is set at 320). The Nexus 7 uses "tvdpi" - i.e. 213 dpi.

Density Independent Pixel

Commonly referred to as dp. This is the virtual pixel unit used when displaying content. The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen. To calculate dp use the following formula:

px = dp * (dpi / 160)

or equivalently:

dp = (px / dpi) * 160

The reason Nexus 7 can show more content than the Galaxy Nexus despite having similar resolutions is this: the dpi of Nexus 7 is lower than Galaxy Nexus.

Galaxy Nexus (320 dpi, 720 pixels wide)

(720 / 320) * 160 = 360 dp

Nexus 7 (213 dpi, 800 pixels wide)

(800 / 213) * 160 = 600 dp

This means that when apps are rendering on the Galaxy Nexus, the width of the screen is actually 360 dp (rendered using 720 pixels). Whereas on the Nexus 7, the width of the screen is 600 dp (rendered using 800 pixels).

Bonus

If your Galaxy Nexus is rooted, you can use an app such as LCD Density Modder and change the DPI of your device to 240. What you'll get is something a lot closer to Nexus 7 in a smaller package. On the left is a screenshot of the device at 240 dpi. You'll notice we can see a lot more content when the DPI is lower.

Galaxy Nexus at 240 dpi Galaxy Nexus at 320 dpi

Nothing to do with PPI

The other answers mention PPI. The amount of content displayed has nothing to do with the PPI of a device. Though commonly, vendors select the DPI that is closest to the PPI of the device. (e.g. Galaxy Nexus has a PPI of 316, but a DPI of 320, where as Nexus 7 has a PPI of 216, but uses a 213 DPI).

Further Reading

http://developer.android.com/guide/practices/screens_support.html

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Thanks for this, nobody else actually answered the question I was asking. –  zacharyalexstern Jul 8 '12 at 4:02
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This is a good answer overall, but the "nothing to do with PPI" paragraph makes a false distinction between DPI and PPI. See my comment on Mohammed Essam's answer. –  Wyzard Jul 8 '12 at 13:43
    
Hello. I just don't understand a word of what you're saying. You assume that the more the dpi is low, the more you can show. But when you have 100 dot per inch, you just show less informations on an inch that when having 200 dot per inch. And also, if the default density is set near to the device ppi, you can't do better, even modifying the value, because as far as I know, yes one dot can be displayed on many pixels, but a pixel cannot display more that one dot. –  Oliver Sep 15 '12 at 11:07
    
Uhhh, do this apply to desktop screens ? –  Oliver Sep 15 '12 at 11:10
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Actually the Nexus 7 has 213 DPI, and is 600x961 dp units. See plus.google.com/105051985738280261832/posts/6eWwQvFGLV8 –  beetstra May 2 '13 at 14:18

Sorry for the stupid answer, but: the Galaxy Nexus makes everything bigger.

For example, the small letter 'a' can have a width of 30 pixels on the Galaxy Nexus, while it only has 20 pixels on the Nexus 7. This way, more letters can fit on the screen. The reason why they appear to be the same size (e.g. 3mm if you put a ruler on the screen) is, as the others said, pixel density. Basically, pixels are bigger, physically, on the Nexus 7.

The reason why the Galaxy Nexus makes everything bigger is so that you can actually use it without keeping it an inch from your face. If the letter 'a' would have a width of 20 pixels, like on the Nexus 7, it would be too small to read comfortably (because pixels are much smaller).

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I understand that, that's not my questioin. –  zacharyalexstern Jul 8 '12 at 4:00

Showing the same amount of content on a 4.6" screen would make it prohibitively small in most cases. You wouldn't be able to read it, so putting that much content on the screen just doesn't make sense. Resolution determines how many pixels you can display, but one pixel is not the same size on every screen. Making content usable and readable requires you to use up more pixels on a smaller screen because they are more densely packed.

For a good comparison, open a web page on a Galaxy Nexus and zoom all the way out. The same page viewed on a 14" (or such) monitor with similar resolution would be no problem, but the text is nearly indecipherable on your phone.


From the standpoint of "how is this accomplished technically" - it largely depends on how an app is written. By default, Android will simply scale the interface on to the larger screen, which may or may not cause more data to be visible (consider a scrolling list, for example: more items would be visible on a larger screen). That's the most basic scenario.

It's also possible, however, for a developer to define entirely different layouts based upon screen size or density. Therefore, the layouts on a 7" device may be completely unrelated to the layouts on a 4" device or 10" device. This gives developers a lot of flexibility to create richer UIs for tablets (and other such devices) while keeping the phone UIs useable. This is covered in length on Android's developers site.

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Was going to say, ironic that Google are supporting the iPad for their Google+... that Glass demo with Brin was something else though... :D –  t0mm13b Jun 28 '12 at 0:26
    
I understand WHY it's done, my question is more how. E.g. is it just a matter of scaling? –  zacharyalexstern Jun 29 '12 at 21:22
    
@zacharyalexstern: That depends on how the app is written, then. You can write an app to use entirely different layouts on screens of different sizes if you want, so it isn't necessarily just "scaling" in the typical sense. Or, you can let the app just scale if you want. There's a fairly sizable set of documentation dedicated to this on the Android developers site but that's a pretty basic summary. –  eldarerathis Jun 29 '12 at 21:29

That's because the pixels per inch (PPI) is different between them. The higher the PPI, the higher the quality but at a cost of (relative) smaller screen size. So the Nexus 7 has 216 pixels per inch while the Galaxy Nexus has 316 pixels per inch. The resolution isn't everything, you also have to consider the density of the pixels.

High PPI values have the advantage that it's HD but it also has a disadvantage which is a smaller screen size (at a persistent resolution).

You can read more about PPI here.

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I don't see what PPI has to do with screen real-estate. Assuming no scaling, the Galaxy Nexus should have roughly the same screen real-estate as the Nexus 7, things just should appear smaller on screen. –  zacharyalexstern Jun 29 '12 at 21:21
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@zacharyalexstern, PPI is relevant because it determines font scaling. 12-point text is supposed to be one-sixth of an inch tall (72pt = 1in), which corresponds to 36 pixels on the 216ppi Nexus 7, and about 53 pixels on the 316ppi Galaxy Nexus. Other UI elements are scaled based on PPI too. –  Wyzard Jun 30 '12 at 0:08
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Basically, the UI elements are scaled to appear with a consistent physical size across devices. That's why you can fit more of them on a device that's physically larger. –  Wyzard Jun 30 '12 at 0:12
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@zacharyalexstern I can't put it better than Wyzard, so I won't. I'm just backing him up because you seem adamant that PPI has nothing to do with the screen real estate. I promise you to the contrary, it has everything to do with screen real estate. You are correct that two 1280x800 screens have the same number of pixels. But all of the Android components are scaled to pixel density. Have you programmed for Android? Is the term dp familiar? –  David Cowden Jul 4 '12 at 2:56
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@DerekKwok, DPI is a printing term that's not really applicable to computer displays. When it's used in relation to computer displays, it's generally a synonym for PPI, because the image is made of pixels, not dots. –  Wyzard Jul 8 '12 at 13:41

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