Viewport

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Definition

The term viewport refers to the size of a window or visible area on a screen. In general, this term is used for displays on mobile devices such as smartphones and tablets.

A more specific meaning of the term viewport refers to a meta element in HTML 5, which plays a crucial role in mobile optimization. The element scales the displayed content so that the size of the screen can be used efficiently. In this case, the meta element viewport ensures that all content is equally legible and displayed correctly and completely on screens of different sizes. The viewport element adapts web pages to the screen’s length and width so that mobile browsers can display the entire content correctly.

General information about viewports

Thanks to the viewport, websites on mobile devices are not displayed in the same way as on a desktop screen. Users do not have to zoom in but can view the content of a page in a way that matches the small display. Viewports as meta elements (in combination with responsive web design) help web browsers to break up the pages and reassemble them on small screens in a way that enables users to receive a meaningful and readable image. Viewports thus have the task of preventing display problems by determining output formats that are tailored to the respective mobile device.

Functionality of the viewport in HTML code or in a CSS file

You can integrate viewports in your HTML files in two different ways: either directly in the document or in a referenced CSS file, whereby the syntax of these two alternatives only slightly differs.

If you want to include the viewport directly into your HTML file as a meta tag, you can use the following code:

<meta name=viewport content="width=device-width, initial-scale=1">

In this case, the width is defined so that it adapts to the respective device’s screen width (width=device-width). Initial-scale stands for the initial zoom factor and signals that your page is to be displayed 1:1 on the screen of a mobile device.

You can also use a viewport to define the height and configure a minimum and/or maximum zoom factor. In addition, the meta tag can prevent users from being able to zoom (user-scalable=no), which is especially useful for apps.

If you specify the viewport in a CSS file instead, you should put it right at the beginning of the file to ensure a correct display.

Possible difficulties

The main difficulty with viewports is that there is a growing number of mobile devices with different dimensions. However, in order to achieve an optimal display on all available devices, there are various tools and software to check the correct display on standard mobile devices. Such tools, for example, are the iOS MIH-Tool, Ghostlab and Adobe Edge Inspect. The latter is also available for Windows. In addition to these test tools, we recommend you to perform real tests on your own smartphone.

Another difficulty is the pixel density. After all, it is not the size of the display, but rather the depth of the pixel display that is decisive for the display on mobile devices. Although pixels are constant units, mobile devices often have a greater density of pixels than older computers. For this reason, it is important for developers to consider how much content should be displayed on a display and whether scaling makes sense.

Practical relevance

Viewports should be specified either in HTML code or in a CSS file for all websites to ensure that they can be displayed on mobile devices appropriately. Especially in the context of responsive web design, a viewport is indispensable and has become the standard for mobile optimization. All website operators who want to provide their users with pleasant and undisturbed reading and surfing experiences should address this topic since the number of mobile users is continuously increasing.

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