As a user I want to see where the air sensors are on a map

[tjohnson-scottlogic]

so that I can decide whether or not a sensor should be used or not.

The ECharts site has examples of maps, including an air pollution one (but other libraries could be used).

Acceptance Criteria

• City view includes a top-down map and the sensor locations are indicated (all sensors in the database for that city)
• Ideally with open source mapping (e.g. Open Streetmap)