Spatiotemporal characterization of urban activity and environment with imagery and deep learning
Bibliographic record
Abstract
BACKGROUND AND AIM: There are limited data on human activity and the environment needed to inform policies and target infrastructures to improve the health and wellbeing of residents in cities in sub-Saharan Africa, the world’s fastest urbanising region. METHODS: We collected a bespoke dataset of 2.10 million images in Accra, Ghana, captured at five-minute internals over ~15 months at 145 representative locations. We retrained a convolutional neural network using a manually labelled subset of images to identify people (including street vendors) and 18 objects – categorised into large vehicles, small vehicles, two wheelers, objects from the market, refuse and animals – that collectively represent important features of human activity and the environment in the city. RESULTS:We identified 23.5 million of these objects in our dataset. Of these, 9.66 million (41%) were humans, followed by cars (4.19 million; 18%). We found strong correlation among the number of people, large vehicles and market-related objects, which were typically captured in the business and commercial core and high-density residential areas; moderate correlation between these three categories and small vehicles; weak correlation with two wheelers; and inverse correlation with refuse and animals which were more common in the peripheral areas of the city. The frequency of objects changed throughout the day with the extent of variation dependent on the type of object and location. There were noticeable reductions in the number of people, vehicles and market related activity in commercial and business areas during the Covid-19 lockdown, but smaller reductions observed in high-density residential areas. CONCLUSIONS:Contextual adaptation of computer vision tools can reduce the global gap in data on cities to advance sustainable and healthy urban development. Our data and approach have the potential to be applied to a range of urban environmental topics, including estimating road-traffic volume/flows and identifying sources of air and noise pollution. KEYWORDS: Big data, imagery, deep learning, built Environment; covid-19; traffic-related
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".