Definition
1. In general legal usage, a given fact, premise, or first principle upon which reasoning, argument, or legal inference is built. The singular form of "data."
2. In old conveyancing and Latin legal instruments, "datum" signified "given" or "dated" — appearing in formal phrases such as "datum apud London" (given at London) to indicate the date and place of execution of a deed or instrument.
3. In surveying and related legal contexts (boundary disputes, land descriptions, easements), a datum is a fixed reference point, line, or plane from which measurements of elevation, position, or distance are calculated. The "datum line" is the baseline from which vertical or horizontal measurements are taken.
Common Language
Modern common usage (Wiktionary): Something known or assumed as fact, made the basis of reasoning or inference; the singular of data; in surveying, a point, line, plane, or surface used as a reference for measurements.
Historical common usage (Webster's 1913): Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based — used chiefly in the plural. In surveying, the datum line is the horizontal or base line from which measurements are taken.
The common and legal meanings overlap substantially, but researchers should note a specific gap: ordinary usage has nearly abandoned "datum" as a singular, defaulting to "data" even when referring to a single item. Legal instruments — particularly older survey descriptions, title documents, and engineering records incorporated into land-use litigation — preserve the singular form with technical precision. A "datum" in a boundary survey is not merely a fact; it is a defined and often certified reference standard (such as the National Geodetic Vertical Datum) with legal consequences for property descriptions and regulatory compliance.
Common Confusion
"Datum" and "data" are the singular and plural forms of the same Latin root, but legal documents do not always treat them consistently. Modern drafting frequently uses "data" as a collective singular, making older instruments that distinguish "a datum" from "the data" potentially confusing. Additionally, the conveyancing sense of "datum" (a date or the act of giving) is wholly distinct from the surveying sense; both can appear in documents relating to real property, and conflating them produces serious misreadings. A phrase like "datum apud London" records when and where an instrument was executed — it says nothing about a reference elevation or measurement baseline.
Why It Matters in Research
Researchers encounter "datum" in at least three distinct documentary contexts, each requiring different handling.
First, in Latin-language or Law Latin instruments (medieval through early modern), "datum" functions as part of the dating clause. Burrill's entry — with citations to Coke on Littleton and Perkins — situates this usage in formal deed practice. Researchers working with early English or colonial American conveyances should read "datum" in closing clauses as equivalent to "given" or "dated," not as a factual premise or a surveying term.
Second, in pleading and jurisprudential writing, "datum" appears in the logical sense: a conceded or stipulated fact from which legal conclusions are drawn. This usage is more common in 19th-century legal treatises and appellate opinions than in modern practice, where "stipulated fact," "given," or simply "premise" tends to substitute.
Third — and of greatest practical importance for contemporary research — "datum" appears as a precise technical term in land survey records, engineering documents, floodplain maps, and regulatory instruments incorporated into real property titles, zoning disputes, environmental litigation, and eminent domain proceedings. Here "datum" refers to a specific geodetic or vertical reference standard (e.g., NGVD 29, NAVD 88). Misidentifying which datum a historic survey used can produce significant discrepancies in elevation or boundary determinations. Researchers connecting survey records to modern legal disputes must confirm which datum was operative when the original measurements were made.
The corpus connections worth tracking: "datum" in its surveying sense links directly to entries on metes and bounds, base line, monument, and benchmark. In its conveyancing sense, it connects to date, deed, and the Latin dating formulas treated under "given."
Historical Dictionary Support
Black's (both editions) and Burrill agree on the core senses: first principle, thing given, and date. Burrill provides the richer treatment, supplying Law Latin context, conveyancing examples, and the maxim "Datur digniori" (it is given to the more worthy), which appears in a priority-of-right context rather than the dating sense — a reminder that "datum" carried multiple valences even within legal Latin.
What the historical dictionaries miss almost entirely is the surveying sense. This absence is not a defect in the sources so much as a reflection of the period: geodetic datum standards were not standardized at the federal level until the late 19th and early 20th centuries, and their legal significance in property and regulatory disputes is largely a modern development. Researchers should not expect historical law dictionaries to resolve questions about geodetic datums; those require consulting surveying standards, FEMA technical bulletins, and land-records practice guides.
Jurisdictional Note
The surveying datum most likely to appear in American land records varies by region and era. Federal geodetic standards (NGVD 29, NAVD 88) apply broadly, but local and state surveys may reference older local datums. Researchers in coastal, floodplain, or mountainous jurisdictions should be especially attentive to which datum underlies elevation certificates and FEMA flood maps, as elevation discrepancies between datum systems can determine regulatory status and property value.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Date (Conveyancing); Metes and Bounds; Survey and Surveyors.