The following tasks are used:
-----------------------------

 Name             | Done | Description
------------------+------+--------------------------------
 map_expander     |   0% | Expands the city map if needed
 household_growth |   0% | Growths a single household
 building_growth  |   0% | Growths building
------------------+------+--------------------------------

- - - - -

Task 'map_expander':
--------------------

The task is responsible for expanding the city map around outer-most zones and
roads. It also initializes the map at first startup (if the city has been
"founded").

For doing this, around the outer-most zones/roads the map is expanded for a
configurable value (default: 100). After the first road has been constructed,
the map is not expanded directly as this would cause permanent expansion of it
which leads to more system load.

Instead, the map is being expanded if the outer-most zone/road has come to
close ("city border threashold") to the border (default: 10). If that value
has reached or surpassed (to close, e.g. by constructing a long road) the map
is expanded (default: 10+100 from outer-most).

- - - - -

Task 'household_growth':
------------------------

The task is responsible for growing all households. The task checks if an empty
zone is given and several pre-conditions are met:

1) A road/path way is nearby (must be given but it will be checked anyway).

2) The zone is not to small (minimum: 2x1 as 1 square must be given as distance
   to the road. This however will be pre-checked by the client.

3) The land value of the resitential zone is not to low (below zero) as this
   hinders that people move in. Please note that some other zones (e.g.
   landfills) may reduce land value around them).

4) The land value is not to high for the citizen (cannot effort to buy the
   zone).

5) There is an empty initial "building" (e.g. hut) on the zone or the existing
   building is a multi-household building and has at least one appartment for
   sale. Please note that rich people prefer low-density and high land-value
   zones over high-density zones except it is an expansive multi-household
   building.

6) The demand for resitential is not below or zero. Below zero means that
   people may give up their home (e.g. high taxes). Vacant appartments or
   buildings are put on sale for the player (for a reduced price).

The task also checks if an existing household has 2 adults of different gender
(1 male, 1 female). Only under this condition reproduction is possible and a
3rd person may be added to it (after about 260-280 days). Adoption is not yet
simulated and may not be added. Please note that this is a city growth
simulation and not a social simulation.

Simulating reproduction conditions is very complex as it depends on many
factors. Both poor and rich people (including "middle rich") are repducing
under same conditions for now.

The task is also responsible for splitting large households (after the child
has become adult) into smaller as adult "children" move out. It may happen that
from the same "parents" adult "children" are moving into one household as
relationships are *NOT* simulated. So even incest is possible and not prevent
by the simulation as this is (again) a city growth simulation.

- - - - -

Task 'building_growth':
-----------------------

The task is responsible for growing buildings up to maximum size which the
current "tech level" and density allows. For constructing a new building some
conditions must be met:

1) A road/path way must be nearby (will be always given but checked anyway).

2) A zone must have minimum size (2x1, as 1 square is needed for distance to
   road). This should be pre-checked by the user's client.

3) No other building is already constructed on the zone, only one building per
   zone is possible.

4) The building type depends on "tech level" and density setting of the zone.

Expansion of an existing building depends on other conditions:

1) The bulding has not reached maximum size, depending on "tech level" and land
   value. E.g. rich people will likely build a villa on the zone while poor
   people may only build a small simple house on it.

2) Zone density must be high enough to allow more stores being added, this has
   a maximum depending on "tech level" and land value, see above.

3) Demand for resitential is high enough, if nothing is demanded, no new
   buildings are constructed and households are funded or expanded.

4) A household has 3 or more adult members and they wish to move out.

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