An economist is tasked with estimating the relationship between the real wage level and the unemployment rate for a country. They are considering two potential data sources:

1. National Time-Series Data: A dataset containing the national average real wage and the national unemployment rate for each of the last 40 years.
2. Local Cross-Sectional Data: A large survey dataset from a single, recent year, containing information on individual wages and employment status for people across hundreds of distinct local labor markets (e.g., cities or regions) within the country.

Analyze these two approaches. Explain why economists typically prefer the second approach (using local cross-sectional data) to estimate this specific economic relationship. In your answer, contrast the strengths of the local data with the potential weaknesses of the national time-series data for this purpose.