YearSpans

Yearspans are contiguous intervals defined by a starting calendar year and an ending calendar year. They describe a period rather than a single year, and the endpoints are typically inclusive, so a yearspan of 1990–1995 covers six calendar years: 1990 through 1995. The concept is used to summarize, compare, and visualize time periods that share characteristics or events.

Notation and scope vary by discipline. Commonly, yearspans are written as start–end (for example, 1776–1783) or described in phrases such as “from 1990 to 1995.” They can apply in history, archaeology, demography, literature, genealogy, and data visualization. In some contexts a yearspan may be open-ended, as in 2010–present, or may be anchored to larger units such as decades, centuries, or eras.

Calculation and interpretation are straightforward but context-dependent. The length of a yearspan is end − start + 1 years. The midpoint year is often used for visualization or labeling, computed as start + floor((end − start) / 2). Yearspans help compress information, but they can obscure variation within the period and depend on stable calendar conventions.

Limitations and variations exist. Historical dating may involve uncertainties (circa dates, radiocarbon calibrations) and calendar reforms (Julian to Gregorian transitions) that affect endpoints. Different conventions may treat endpoints inclusively or exclusively. In practice, yearspans are tools for organizing temporal information, rather than strict measurements of time.

See also: era, epoch, decade, century, timeline, regnal year.