Tutorial 3: Playing with more than one district

Until now, we limited th examples to one-district systems. But in the real world, systems contains multiple divisions. In this tutorial a new type of node will be introduced: the group of districts or nodes.

UK - General election (complete schema)

Let’s go back to the UK - General election (Caerfyrddin) tutorial. Then, we defined the system for just one constituency. Now, we will include all constituencies:

1. Create a group of nodes, and put our constituency (Caerfyrddin) into its divisions (candidates are not shown):

   name: 2024 UK General election
   type: group
   divisions:
   - name: Caerfyrddin
     method: first_past_the_post
   

2. Add the remaining 649 constituencies:

   name: 2024 UK General election
   type: group
   divisions:
   - name: Amber Valley
     method: first_past_the_post
   ...
   - name: Caerfyrddin
     method: first_past_the_post
   ...
   - name: West Tyrone
     method: first_past_the_post
   

3. Since all the constituencies share the same method, it will be easier if we define it once for all the divisions:

   name: 2024 UK General election
   type: group
   method: first_past_the_post
   divisions:
   - name: Amber Valley
   ...
   - name: Caerfyrddin
   ...
   - name: West Tyrone
   

   Now, all the constituencies will inherit the method defined by its parent. There are other properties that are inherited by children (see NodeContext).

4. If we want to get an aggregated result (for example, get a result grouped by parties), a criterion can be added to the root node:

   name: 2024 UK General election
   type: group
   method: first_past_the_post
   # enable aggregated result
   aggregate: yes
   # group seats by parties
   groupby: "alliance"
   divisions:
   - name: Amber Valley
   ...
   - name: Caerfyrddin
   ...
   - name: West Tyrone
   ...
   

   Aggregated results can be controled by using the properties aggregate and groupby.

Spain - Andalusian regional election

Andalusian Parliament electoral system uses 8 districts, one per province. Each distrct apportions a number of seats using the highest averages method with d'Hondt divisors. Candidates with less votes than the 3% of total valid votes in the district are excluded from the apportionment for that district.

The system for the Spanish Parliament would be exactly the same, but with 52 leaf districts.

name: Parlamento Andaluz 2015
type: group
method: highest_averages
method_params:
    divisor_f: dhondt
exclude: "valid_votes < 3%"
divisions:
-   name: Almería
    seats: 12
-   name: Cádiz
    seats: 15
-   name: Córdoba
    seats: 12
-   name: Granada
    seats: 13
-   name: Huelva
    seats: 11
-   name: Jaén
    seats: 11
-   name: Málaga
    seats: 17
-   name: Sevilla
    seats: 18

Since include and exclude restrictions are inherited by chldren, the threshold is defined once by the root node, but applied at each province. A restriction that does not reference to node will use the district where it is been used as reference.