City.fromMap constructor
Factory method to create a City object from a Map.
The map
must contain the keys: 'name', 'population', and 'area'.
Implementation
factory City.fromMap(Map<String, String> map) {
return City(
name: map['name']!,
population: map['population']!,
area: map['area']!,
tehsils: map['tehsils']! as List<String>,
);
}