Cellxgene Census

# CZ CELLxGENE Census

## Overview

The CZ CELLxGENE Census provides programmatic access to a comprehensive, versioned collection of standardized single-cell and spatial transcriptomics data from CZ CELLxGENE Discover. This skill enables efficient querying and analysis of public Census releases without downloading whole datasets first.

The Census includes:
- **217+ million total cells** and **125+ million unique cells** in the 2025-11-08 stable LTS release
- **1,845 datasets** in the 2025-11-08 stable LTS release
- **Human, mouse, marmoset, rhesus macaque, and chimpanzee** data in the current schema
- **Standardized metadata** (cell types, tissues, diseases, donors)
- **Raw gene expression** matrices and source H5AD lookup/download helpers
- **Pre-calculated summary counts, embeddings, and spatial data**
- **Integration with AnnData, Scanpy, TileDB-SOMA, TileDB-SOMA-ML, and other analysis tools**

## When to Use This Skill

This skill should be used when:
- Querying single-cell expression data by cell type, tissue, or disease
- Exploring available single-cell datasets and metadata
- Training machine learning models on single-cell data
- Performing large-scale cross-dataset analyses
- Integrating Census data with scanpy or other analysis frameworks
- Computing statistics across millions of cells
- Accessing pre-calculated embeddings or model predictions

## Installation and Setup

Install the Census API:
```bash
uv pip install "cellxgene-census==1.17.*"
```

For spatial workflows:
```bash
uv pip install "cellxgene-census[spatial]==1.17.*" "spatialdata[extra]>=0.2.5"
```

For PyTorch model training, use TileDB-SOMA-ML. The old `cellxgene_census.experimental.ml` loaders are deprecated:

```bash
uv pip install "cellxgene-census==1.17.*" tiledbsoma-ml
```

## Core Workflow Patterns

### 1. Opening the Census

Always use the context manager to ensure proper resource cleanup: