Põhijoone

Põhijoone is the Estonian term for the baseline in typography and typesetting. It designates the imaginary line on which the main body of most letters sits. Most lowercase letters have their bottoms aligned with the baseline, while letters with ascenders (such as b, d, h) rise above it and letters with descenders (such as g, p, y) fall below it. The baseline thus acts as a visual anchor and reference for vertical metrics in a font.

In font design and digital typesetting, metrics are defined relative to the baseline. The distance from the baseline to the top of the tallest glyph is called the ascent, and the distance from the baseline to the bottom of the lowest glyph is the descent. The line height (or leading) is the distance between baselines of successive lines, and the line gap is the portion of that distance that is extra space. These measurements ensure consistent alignment and rhythm across lines of text.

In practical use, the baseline is essential for layout, alignment, and grid systems in both print and web design. CSS line-height, for example, governs the distance between baselines of adjacent lines, reflecting the ongoing importance of the baseline in digital typography.

Põhijoone is a fundamental concept in Estonian typography and is commonly discussed in resources on fonts, typesetting, and page layout.