Concept: types in grapher data model

[larsyencken]

Problem

• The data processing in Grapher on the client is more complex than it needs to be because we don't know types
• Visualisation is more complex than it needs to be because we don't know types
  • E.g. we don't know hierarchy between categorical variables (World vs Europe vs Sweden)
  • E.g. we don't know that a categorical variable is in fact ordinal (Low Income, Middle Income, Upper Income)
  • E.g. we can't auto-pick the best color palette because we don't know enough about the categorical variable

Proposed solution

• Add a type system to Grapher's data model that includes numeric, geo, and ordinal types (with optional ordering)

[larsyencken]

@pabloarosado Just a head up from the ETL side that this is something that we'd like to move towards.

[sophiamersmann]

See #3376 for a list of things that we could improve if we knew data types