Three key underlying questions must be addressed in any approach:
1) What is more precisely meant by upgrading? (parameters, scope, components);
2 ) What is scaling-up? (how can you tell it when you see it?);
3 ) What criteria do you use to judge success of scaling-up? (time to implement is a key indicator, but also % of people served at X standard? poverty and health situation improved?).
What is the minimum policy framework for upgrading? Security of tenure clearly is necessary, and what else? The fundamental assumption is that scaling-up slum improvement is a necessary and needed action.
Strategies may vary according to:
a - Sophistication of government: Low end governments have capacity limited to more basic techniques, simpler components, and simpler implementation.
High end governments have capacity for relatively sophisticated techniques, high-end components, and more complex implementation.
b - Level of demand: a very high and growing demand would probably require a conceptual shift; and conversely, a more limited demand perhaps allows expansion and improvement of current practices.