# datum (1-datum.org)

A single piece of information. One fact or observation. The singular form of "data," though many people say "data" for both one and many.

## What a model may hear
- single data point (statistics and machine learning): treat the input as one training example, one row, or one observation in a dataset
- geodetic reference frame (geography and cartography): assume the user means a coordinate system or map reference like NAD83 or WGS84
- database record (databases and information systems): interpret the request as about one record, tuple, or entry in a table
- linguistic object (formal grammar and logic): treat it as a minimal unit of meaning or a primitive value in a formal system

## Where people and models part ways
- Says: "I need a datum for my report"
  Means: one fact or number to include
  May be taken as: search for geodetic datums or database schemas
  Say instead: "I need one fact or statistic to cite in my report"
- Says: "Store this datum"
  Means: save this one piece of information
  May be taken as: design a database table with one row or ask for a primary key
  Say instead: "Save this single piece of information for me"
- Says: "What datum should I use?"
  Means: which fact is correct
  May be taken as: explain map projection coordinate systems
  Say instead: "Which of these facts is the correct one to use?"
- Says: "The datum shows an error"
  Means: the number or fact is wrong
  May be taken as: diagnose GPS coordinate reference system errors
  Say instead: "This single number or fact appears to be wrong"

## Tips
- Say "one fact" or "single piece of information" instead of "datum" when you do not mean maps or databases
- If you mean geodesy, say "coordinate system" or "map datum" explicitly
- Use "data point" when speaking to a model about statistics or machine learning
- Say "one row" or "single record" for databases, not "datum"
- If you must use "datum," add context like "one datum from my survey" to steer away from geodesy

## Often confused with
- data: plural or mass noun, not singular
- dataset: a collection, not one item
- datums: plural of map reference frames, not facts
- data point: more common in statistics and clearer to models
- datum plane: a reference surface in engineering
- metadata: data about data, not a single fact