MapBiomas Urban Areas Maps: contribution to urban analysis in Brazil

MapBiomas land cover and land use annual maps of Brazilian territory are produced in a collaborative and low-cost method and are freely available at project's platform (http://mapbiomas.org). Since 2016, when Collection 1 was published, each year MapBiomas initiative releases a new Collection, with improved methodology and extended time series. Current Collection 7 presents maps from 1985 to 2021. Urban areas (UA) are a cross-cutting theme within MapBiomas. UA are areas with predominance of significant density of buildings, roads and infrastructure.

Following the general methodology of MapBiomas, UA classification adopts a supervised machine learning method applied to Landsat imagery with extensive training datasets. A specific random forest classification model is built to each tile (522 valid tiles) and year (37 years). Spatial and temporal filters are applied post-classification. Last step is the integration of UA data with other themes. Preliminary accuracy assessment based on samples visually and independently interpretated points out that commission errors are less than 10% while omission errors decrease from the first years (45% in 1985) to the final years (16% in 2018). Detailed procedures are in the Algorithm Theoretical Basis Document, available at the project's platform and scripts are published at UA Github repository.

In 2021, UA correspond to 3,7 million hectares or only 0,44% of Brazilian territory. From 1985 to 2021, UA expanded at a rate of 3,20% per year. Population between 1980 and 2021 have grown at 1,43% per year. Integrated analysis of urban expansion, population and urban hierarchy shows a densification process (population grows at higher rates than UA) in metropolises, while the opposite process occurs in medium and, with more strength, in small cities. MapBiomas data also enable the assessment of land covers transformed into UA: 45% of UA in 2021 were farming land and 14% were natural vegetation in 1985.

Yearly MapBiomas UA maps are a valuable contribution to urban analysis based on comparative urban expansion analysis among distinct regions or evaluation of intra-urban expansion in risk areas or informal settlements, for example. Also, this dataset can be used as an input to climate or hydrological modellings, and to impact assessments related to energy consumption or transportation.