Long-Term Transformation of Apartment Unit-Size Composition in South Korea: A Nationwide Linked-Data Analysis

Research on long-term changes in Korean apartment units has generally relied on limited case samples. This study constructs a nationwide linked dataset spanning apartment completion cohorts over multiple decades by connecting the Korean Apartment Management Information System (K-apt) with unit-type metadata from Naver Real Estate. A conservative entity-matching procedure linked 13,961 of 19,424 K-apt apartment complexes to 13,959 unique Naver complex identifiers, yielding 60,803 unit-type records and 60,801 valid exclusive-use area observations. The geographically nationwide linked sample is dominated by sale-oriented complexes and does not constitute a dwelling-weighted census of the national apartment stock. We combined descriptive cohort analysis and threshold-heaping tests with complex-level nonlinear and quantile-regression models, interaction tests, and sensitivity analyses. Unit types were strongly concentrated immediately below 60 and 85 m2: 16.4% fell within 59–<60 m2 and 31.8% within 84–<85 m2, with local heaping ratios of 26.0 and 63.3. Across integer boundaries from 31 to 150 m2, 85 and 60 m2 ranked first and second in heaping. Temporal patterns showed upper-tail expansion during the 2000s followed by reconcentration after the early 2010s. The findings indicate persistent size standardization alongside growth in platform-recorded unit-type variants, without directly establishing greater floor-plan morphological diversity.