Maps are data in themselves. However, map data also includes related data that the maps showcase. For instance, real-time traffic, current and historical political boundaries, active weather patterns, crime statistics, infrastructure and points of interest.
This data generally starts with public records or satellite images. Afterward, users add relevant data. For example, fleet tracking software records GPS and location data on vehicles and combines it with road maps. Or meteorological data is recorded and county boundaries overlaid onto it.
Naturally, this data ends up as a map of some kind—topographical, isochrone, cluster, etc. However, unless built or collected as an image, the map started as simple data points in columns and then were integrated into maps.
The uses of this data are enormous. Governments use it to address crime in certain areas or update aging infrastructure. Businesses use it to locate new store locations. Individuals use it to prepare for adverse weather or quickly get through traffic. In short, this data can help resolve almost any human concern.
With the massive amount of freely available data, testing the accuracy of most maps is not difficult. For maps that update in real time, however, you should check that your map connects to a live updating (clean) feed.
You may also use government geological standards and guidelines to ensure the quality of your data. See, for example, the FGDC (Federal Geographic Data Committee) standards.
WRI: Maps & Data
Datawrapper Blog: Chartable
Karachi Futures is a research initiative and tech company aiming to understand the social and economic problems of Karachi in a deeper quantitative and qualitative sense. The platform currently focuses on factors that influence environment, such as green cover and spaces, land surface temperature, urban heat island (UHI) effect, and urban build, but will bring upon more metrics to analyse Karachi.
PT Profit: Karachi Futures quests to map port city through data