Writing

Writing.

Field notes on building data and AI systems: what got built, what broke, and what it changed.

Could a free satellite have called Amsterdam's quay-replacement schedule?Amsterdam is replacing 200 km of historic quay walls, guided by divers and engineers. The Netherlands publishes a free millimetre-precision InSAR subsidence map. I put the free signal on trial: pre-registered prediction, four failure directions tested, and a mechanism-tested null (AUC 0.49) that turned out to be the interesting answer.

The model inside FishFinder: ResNet50, fine-tuning, and when to freeze layersFishFinder classifies 63 Dutch fish species from ~3,000 photos. That only works because the model doesn't start from zero: a pretrained ResNet50, fine-tuned with layer-wise learning rates. Here is how transfer learning, freezing and discriminative LRs actually work, with the real numbers.

One JSON per Published Number: the Pipeline Contract That Made Adversarial Review CheapHow a one-script, one-JSON, one-figure contract turned a full methodology overhaul of the metro capitalization paper into a single working session instead of a rewrite.

"Pinned" should mean bytes-identical: a snapshot-guard operatorAn operator that treats pinned inputs as a contract: if the bytes changed, the pipeline should refuse to pretend otherwise.

A custom DuckDB operator: SQL-first ingestion in AirflowBuilding a custom Airflow operator that makes DuckDB the ingestion engine: SQL-first, testable, and cheap.

Research pipelines are production systems: a seriesWhy research data pipelines deserve production discipline: the series opener.

Parameters belong in the schema, not the filenameA pre-arXiv audit found the paper and its artifacts disagreeing about which hyperparameters produced the headline number, and nothing in the data model could settle it.

Seven Cities, 42,000 Observations, and a Headline That Hung on One Modeling ChoiceA phase-decomposed DiD across seven cities, and how one fixed-effects specification choice moved the headline result.