Participatory mapping and food‐centred justice in informal settlements in Nairobi, Kenya

Food vendors are pivotal in the local food system of most low‐income informal settlements in Nairobi, Kenya, despite being seen as an obstruction and as agents of disease and filth by city authorities. This paper explores the geography of these foodscapes – defined as public sites of food production and consumption – in selected low‐income settlements in Nairobi, focusing on the interaction of food vendors with their surrounding environment and infrastructure services. The research uses participatory geographic information system tools, including food mapping with mobile apps and high‐resolution community aerial views with balloon mapping, to capture and contextualise local knowledge. The community mappers collected data on 660 vendors from 18 villages in Kibera, Mathare, and Mukuru, and situated them on multi‐layered synoptic geographic overviews for each settlement. The resulting data on hazardous areas in relation to food spaces and infrastructure provision allowed local communities to prioritise areas for regular clean‐up activities and assisted advocacy to improve these places in cooperation with local authorities. These multiple visual representations of foodscapes make local food vendors, and the risks they face, visible for the first time. Reframing their “right to safe food and environment” from a social and environmental justice perspective allows local communities to put their experiences, knowledge, and challenges faced at the forefront of urban development planning, policy, and practice

High resolution, annual maps of field boundaries for smallholder-dominated croplands at national scales

Mapping the characteristics of Africa’s smallholder-dominated croplands, including the sizes and numbers of fields, can provide critical insights into food security and a range of other socioeconomic and environmental concerns. However, accurately mapping these systems is difficult because there is 1) a spatial and temporal mismatch between satellite sensors and smallholder fields, and 2) a lack of high-quality labels needed to train and assess machine learning classifiers. We developed an approach designed to address these two problems, and used it to map Ghana’s croplands. To overcome the spatio-temporal mismatch, we converted daily, high resolution imagery into two cloud-free composites (the primary growing season and subsequent dry season) covering the 2018 agricultural year, providing a seasonal contrast that helps to improve classification accuracy. To address the problem of label availability, we created a platform that rigorously assesses and minimizes label error, and used it to iteratively train a Random Forests classifier with active learning, which identifies the most informative training sample based on prediction uncertainty. Minimizing label errors improved model F1 scores by up to 25%. Active learning increased F1 scores by an average of 9.1% between first and last training iterations, and 2.3% more than models trained with randomly selected labels. We used the resulting 3.7 m map of cropland probabilities within a segmentation algorithm to delineate crop field boundaries. Using an independent map reference sample (n = 1,207), we found that the cropland probability and field boundary maps had respective overall accuracies of 88 and 86.7%, user’s accuracies for the cropland class of 61.2 and 78.9%, and producer’s accuracies of 67.3 and 58.2%. An unbiased area estimate calculated from the map reference sample indicates that cropland covers 17.1% (15.4–18.9%) of Ghana. Using the most accurate validation labels to correct for biases in the segmented field boundaries map, we estimated that the average size and total number of field in Ghana are 1.73 ha and 1,662,281, respectively. Our results demonstrate an adaptable and transferable approach for developing annual, country-scale maps of crop field boundaries, with several features that effectively mitigate the errors inherent in remote sensing of smallholder-dominated agriculture