Nighttime satellite data acts as a proxy for economic activity. In view of COVID-19 pandemic and its impact on economic activity, the Urban Expansion Observatory along with MapDataLab analyzed daily night light data of 11 impacted cities around the globe. We used the Suomi National Polar-orbiting partnership Visible Infrared Imaging Radiometer Suite (VIIRS) sensor which provides global daily night light measurements. We analyzed the daily VIIRS night light data from November 2019 to March 2020 and created a monthly average product after removing the moonlight illumination effects and by excluding imagery with excessive cloud cover. We created bounding box around each city which covers urban agglomeration and calculated a monthly average illumination for each city region. In most of the cities, we see dramatic fall in nighttime illumination in the month of March indicating severely depressed economic activity.
It presents maps and measures of the recent, as well as the long-term, expansion of cities having a population of 100,000 people along with information regarding its quality, the performance of the housing sector, and the state of regulatory regimes, the areas built between 1990 and 2019 in an easily accessible format. It also provides authoritative data, information, and advice on current and emerging urbanization trends and conditions of a stratified global sample of 200 cities.
The aim of this study is to provide informed analysis to policy makers, public officials, research administrators, and scientists for use in their decision-making processes.
Maps and metrics along with the quality of the growth and expansion of cities are classified into two headings are as follows:
1. Areas and Densities
2. Blocks and Roads
PHASE I: The Mapping and Measurement of Global Urban Expansion
Phase I includes downloading high-resolution Landsat satellite imageries for the years- 1990, 2000, 2010 and 2019 and classifying them to obtain the urban areas in each time period. Urban expansion is measured using their associated metrics- urban extent, built-up area density, fragmentation and compactness of each city for the respective years.
PHASE II: The Mapping and Measurement of Urban Layouts
UXO studies the urban layout of a city by classifying the area into various categories based on their land use types. The process includes identifying the blocks, creation of medians and plot measurement. This analysis along with the population data for each city acquired from United Nations Population Division helps in finding the resulting metrics- the share of land in arterial roads and access to arterial roads, the share of land in streets and the distribution of street widths, the share of land in residential areas in different stages of housing sector evolution (atomistic housing, informal land subdivisions, formal land subdivisions, and housing projects), average block size and the density of street intersections, plot dimensions in land subdivisions and the density of 3-way and 4-way intersections.
For better analysis, the areas falling under open spaces are further classified into various subcategories based on the occupancy of area by each category of open spaces and the atomistic areas are classified as formal or informal based on the quality of housing and infrastructure.
We identify and digitize arterial roads using high resolution Bing imagery throughout the urban extents of the city. It is then used to calculate the 3-way and 4-way intersections, the share of the built-up area within walking distance to arterial roads, the average beeline distance to an arterial road, and the density of arterial roads. All of these measures provide some insight, for the first time, on the availability of arterial roads in cities around the world, as well as on its change over time.
Arterial road is further differentiated into two categories: Wide and Narrow based on their ROW width.
More details can be found here http://www.atlasofurbanexpansion.org/
UXO along with 100 Resilient Cities- Pioneered by The Rockefeller Foundation (100 RC) is helping the cities around the world to strengthen and increase their capacity to survive, face and grow in these challenges.
UXO provides guidance to the cities by projecting the growth in their urban extent in the coming 30 years which provides assistance regarding the urban planning and precautionary measures to be taken by the cities to tackle the problems. For this purpose, few main factors such as Roads, Global Human Settlement Layer (GHSL), Water pixels and Slope Percentage along with the past data are considered in predicting the growth in urban extent.
UXO helps in calculating temporal data of cities’ urban density for creating further planning policies. As a part of the process, building footprint, footprints of all the residential buildings and houses in the residential block (formal and informal) are studied.
Building height provides information about the height of residential buildings based on the number of floors in these structures. The total floor area is the product of number of floors and the building footprint area.
Residential coverage is an important factor in generating urban density of a city because the urban population is more likely to settle and increase in areas under residential use rather than industrial and commercial areas. It gives us the ratio between the area occupied by residential building footprints and total area of the urban extent of the city. Residential coverage of a city is more when the houses or residential buildings are built closer to each other.
In majority of the cases, areas between residential buildings are provided for open spaces and parking lots associated with the residential buildings along with their building footprints. The main objective for computing plot coverage is to get the share of area covered by actual residential building footprint with respect to the total area classified as a residential area.
When the urban extent is calculated, it also includes the Industrial areas and private open spaces along with residential areas hence we calculate residential share which shows the share of the urban extent covered by land under residential use.
The number of people occupying a unit of total residential floor area in a city is called crowding. There is a direct proportion between crowding and urban density of a city. Crowding gives us the relation between total city population by total floor area of the city. It is a product of Living Area Density, Occupancy Rate and Floor Plan Efficiency.
Occupancy rate helps in calculating the residential area which is currently occupied by people living there. All the houses which are vacant because either they are new, on resale or have a same owner living out of the town are vacant and are not occupied by people currently which gives us an estimate of area which can be used for densification of the city. Occupancy rate is the share of total occupied residential units among the total residential units.
Floor Plan Efficiency:
Total floor area is a product of number of floors in a residential building and its footprint. Floor plan efficiency factor is computed to know the share of actual living area out of the total floor area. Information about the living floor area in all the residential structures is gathered from various secondary sources such as architectural floor plans gathered either from World Wide Web or from real estate sites.
For the purpose of analysis, the buildings are categorized into Single Family having their own private entrance, Non-core multi-family including low-rise, medium rise and walkup apartments and core multi-family having a central mechanical shaft with more than eight stories.
UXO has performed the drone mapping process for various sites including Byculla site, a project for TCS having approximately 10 to 12 sites across Maharashtra and for an area where a university in Nashik is going to be built over an open space.
The data required for drone mapping is acquired by flying drones over the site and collecting high-resolution images at a particular time interval. Images captured from drone are then further processed using Pix4D software. Analysis represents the 3D visualization of earth’s surface with the associated R, G, B color scheme representing the elevations such as buildings, etc, volume and capacity of the area using 3D Mesh, DSM and DTM.
Caribbean island country named Grenada is experiencing sea-level rise which is affecting its significant area. UXO along with NYU has an opportunity to assist the local government regarding the urban development and planning the urban policy for the coming 30 years.
For the purpose of analysis, urban area of Grenada for over 30 years is studied. Road layer, cadastre layer, building height analysis and existing land use map is done for the capital city of St. George and for the town of Grenville.
DEM (Digital Elevation Model), contours, watershed maps and drainage mapping is done to provide information about underground water supply, availability and its usability. The main issues which UXO is trying to address are related to sea-level rise, sustainable urban planning and capacity building. After the analysis, we have come to a conclusion that the future urban development is likely to take place in St. David parish and St. George parish mainly because of the availability of the land and these are the areas where the existing clusters are concentrated.
UXO facilitates the creation of interactive maps and applications which provides querying of the spatial information and helps in understanding the underlying pattern of the data. The applications can be customized according to the analysis requirements. We create desktop as well as mobile applications which can be hosted not only on public but also private servers. The data available on the application can be updated within seconds and can also provide 2D as well as 3D visualization of real-time information. Our application building process includes confirming the most efficient design for the application to meet the needs, developing the app and carrying out interrelated steps for deployment of the app and make it ready to use.