and social sciences fields see the most research with regard to Sustainable Development Goal 11, followed by medicine, energy and engineering. Targets, indicators and progress The UN has defined 10 targets and 15 indicators for SDG 11. Targets specify the goals, and indicators represent the metrics by which the world aims to track whether these targets are achieved. Six of them are to be achieved by the year 2030 and one by the year 2020 and three have no target years. Each of the targets also has one or two indicators which will be used to measure progress. Target 11.1: Safe and affordable housing The full title of Target 11.1 is "By 2030, ensure access for all to adequate, safe and affordable housing and basic services and upgrade slums". This target has one Indicator: Indicator 11.1.1 is the "Proportion of the urban population living in slum households". People who live in slums have no access to improved water, access to improved sanitation, sufficient living area, and durable housing. Target 11.1 is to ensure access to safe and affordable housing by 2030. The indicator to measure progress toward this target is the proportion of urban population living in slums or informal settlements. Between 2000 and 2014, the proportion fell from 39 percent to 30 percent. However, the absolute number of people living in slums went from 792 million in 2000 to an estimated 880 million in 2014. Movement from rural to urban areas has accelerated as the population has grown and better housing alternatives are available. A sustainable transportation system considers different socioeconomic groups' travel concerns to achieve the validity of accessibility metrics. According to the Bogota research, transportation and transportation planning should be coordinated with land use planning. Employment and residential areas are relatively concentrated, and urban and suburban settings should be planned and reconstructed in concert. Target 11.2: Affordable and sustainable transport systems The full text of Target 11.2 is "By 2030, provide access to safe, affordable, accessible and sustainable transport systems for all, improving road safety, notably by expanding public transport, with special attention to the needs of those in vulnerable situations, women, children, persons with disabilities and older persons". This target has one Indicator: Indicator 11.2.1 is the "Proportion of population that has convenient access to public transport, by sex, age and Persons With Disabilities". Improving transport systems to refine the use of accessibility is key because