Terminology

Using Cartoj requires several concepts that require more explanation if you're new to geospatial data. There's nothing new here, just an overview of the vocabulary and some links to their origin.

Map

Cartographers almost universally refer to visualizations of spatial data as a map.

Clojure users already use map for two other concepts. First, map as function application for functional programming. Second map as the associative data structure denoted with curly braces {}.

Cartoj tries to use the term "interactive map" to disambiguate. Yes carto/interactive-map is more verbose, but less confusing than the alternative. We don't need a third map.

Features

In geospatial data terms, a Feature is a "spatially bounded thing", an entity with a spatial representation.

The term was originally used in cartography (i.e. "Features of the map"). It has been formalized in both the OGC Simple Features and the GeoJSON standard. The concepts in Maplibre are based on the GeoJSON flavor.

A Feature consists of two parts:

• properties: a dictionary of the feature's attributes. Typically flat, aka columns.
• geometry: the feature's spatial representation in 2D space. Can be a point, line, polygon, or their multipart variations.

Another way of thinking about a Feature: It's like a row in a relational database, with a special column and data type for representing the geometry.

Sources

Sources are the concrete implementation format, the data delivery mechanism. Documentation There are four primary source types:

• vector: Tiled vector data, in the Mapbox Vector Tile format
• raster: Tiled, in standard image formats (PNG, JPG, etc.). These are either inherently raster (imagery) or are vector sources rendered to images server-side.
• raster-dem: Like raster but with a special encoding to define terrain for 3D maps, Mapbox Terrain RGB
• geojson: Not tiled, typically a complete dataset in GeoJSON format

Styles

A MapLibre style is a document that defines the visual appearance of a map: what data to draw, the order to draw it in, and how to style the data when drawing it.

From the Mapblibre Style Spec

Layers

Layers are the main abstraction for building interactive maps. They combine a data source with a style.

One source can be associated with many styles thus many layers. The source layer and the visual layer are decoupled. It's common to have one source with two layers; one for the geometry itself, another for its label.