Geologic maps show where rock units reach the surface. Where
Stratigraphic columns describe the vertical succession of rocks at a place, maps
describe their extent across the landscape. Macrostrat integrates maps made by many
organizations, at scales from individual quadrangles to the whole globe, into a
single queryable, multiscale geologic map of the Earth. It can be explored in the map
interface (/map) and through the API and map tiles (Data services).
Map sources
Each map brought into Macrostrat is a source. A source records the map's bibliographic reference (authors, title, year, publisher, DOI), its license, the URL it came from, and its scale. Macrostrat sorts maps into four scale buckets:
| Scale | Typical maps |
|---|---|
| tiny | Global compilations |
| small | Continental and national compilations |
| medium | Regional and state maps |
| large | Detailed local mapping, such as quadrangles |
A source also has a footprint: the area it covers. Footprints decide where each map is drawn and which map wins where several overlap (see Map compilations).
Each source is identified by a numeric source_id and a short, readable slug.
What a map contains
A map source holds three kinds of geometry:
- Polygons: the units on the map. Each polygon carries the descriptive fields of its legend: a unit name, a stratigraphic name, an age as written by the author, formal base and top intervals, lithologies, and a free-text description.
- Lines: contacts, faults and other linear features, each with a type and name.
- Points: point observations, chiefly structural measurements such as strike and dip.
Polygons that share a description form a legend entry. The legend is the unit of harmonization: matching a legend entry to Macrostrat's vocabulary applies to every polygon drawn with it. The fields Macrostrat expects for polygons are described in Contributing maps to Macrostrat.
From many maps to one
Source maps overlap, disagree at their edges, and describe rocks in their authors' own terms. Three steps turn them into one coherent map:
- Ingestion brings a map's files into Macrostrat and cleans them into the standard structure above (Map ingestion).
- Harmonization matches each legend entry to the Geologic lexicon: stratigraphic names, lithologies and time intervals. This is what lets a user search for "all Ordovician carbonates" across maps made by different surveys decades apart (Linking data).
- Compilation decides which map is shown where, at each zoom level, so that detailed maps appear where they exist and global maps fill in everywhere else (Map compilations).
The result is published as Macrostrat's carto map: one continuous geologic map at several levels of detail, used by Macrostrat's own map interface, by Rockd, and by many other applications. Every polygon in it can still be traced back to the map it came from and that map's original description.
Coverage
Macrostrat currently integrates more than 300 geologic maps containing more than 2.5 million polygons, with global coverage at small scales and detailed mapping where it has been ingested, most extensively in the United States. Major new compilations from the United States, Europe and Japan are being brought in.
