Welcome to City Layers - a digitised participatory tool for urban design. The project proposes a critical and contemporary city-making technology focused on contributing to more egalitarian approaches to urban planning. This app has been developed in collaboration with students, citizens and researchers all interested in democratising and diversifying how cities are formed. Inside City Layers, feel free to use tags, textual comments, photographs, suggestions and votes to articulate your views on a particular urban surrounding. These impressions can include material and immaterial 'layers' of the city, from physical places, to observations, demands and responses. City layers can be added, depending on the phenomena needed and detected by the user. Any user can share personal reflections and thoughts on their desired city forms, and map the urban fabric depending on particular needs. Citizens can add thoughts on how urban places can be improved, or they can immerse themselves in the information on their urban surroundings mapped by others. City Layers seeks to empower citizen engagement to tackle spatial, social and environmental asymmetries and inequalities - increasingly reinforced through city-data processing and urban design. This city mapping app serves as a means of communication between cities and their citizens, generating a contemporary, critical form of data that is collectively generated, managed and cared for.