baselayers

Baselayers, or base layers, are the foundational layer in mapping and geographic information systems. They provide the geographic context for other data and are drawn beneath all overlays and feature layers. In many map applications, the baselayer is the first layer loaded and is designed to be visually neutral enough to support data visibility while conveying essential geographic information such as roads, boundaries, landforms, and place names.

Baselayers can be raster or vector. Raster baselayers consist of pre-rendered images such as satellite imagery, aerial photographs, or shaded relief. Vector baselayers render geographic features as scalable shapes and lines, often used to create stylized basemaps that remain clear at varying zoom levels.

In web mapping, baselayers are usually tile-based. Raster tile layers deliver image tiles, while vector tile layers transmit geometric data that is styled on the client. Mapping libraries like Leaflet, OpenLayers, and Mapbox GL support switching between base layers and overlays. Baselayers may be designed for online services or offline use, cached on the device for performance and reliability.

Data sources and licensing vary. Baselayers come from public, commercial, or open sources. Open data such as OpenStreetMap is commonly used for open baselayers; other providers include Esri, Mapbox, and various government or commercial datasets. Licensing and attribution requirements differ, with many baselayers requiring proper attribution and adherence to terms of service.

Design and usability considerations include maintaining readability of overlaid data, providing appropriate contrast, and optimizing performance through suitable zoom ranges and tile sizes. Examples of common baselayers include OpenStreetMap standard baselayer, Mapbox Streets, Esri World Street Map, Esri World Imagery, and stylized options like Stamen Terrain or Hillshade.