---
session: ses_2b4f
updated: 2026-04-01T21:57:48.280Z
---

# Session Summary

## Goal
Analyze how the SVD Components tab in `explorer.py` computes party positions, focusing on: data loading flow, window_size default, X/Y coordinate computation, and whether positions are individual MPs or party centroids.

## Constraints & Preferences
- Provide exact file:line references for all code paths
- Trace data flow through multiple files and functions
- Answer 4 specific questions about the SVD Components tab implementation

## Progress
### Done
- [x] Analyzed `build_svd_components_tab()` at `explorer.py:2449-2867`
- [x] Traced `load_positions()` at `explorer.py:603-656` — default window_size is "quarterly"
- [x] Traced `load_party_axis_scores()` at `explorer.py:836-853`
- [x] Traced `_load_mp_vectors_by_party()` at `explorer.py:778-832`
- [x] Analyzed `compute_2d_axes()` at `analysis/political_axis.py:131-476`
- [x] Analyzed `compute_party_bootstrap_cis()` at `analysis/political_axis.py:624-695`
- [x] Analyzed `compute_party_centroids()` at `explorer_helpers.py:246-317`
- [x] Documented complete data flow with file:line references

### In Progress
- (none — analysis complete)

### Blocked
- (none)

## Key Decisions
- **Window size**: The SVD Components tab uses `"quarterly"` as the default window_size (via `load_positions()` at line 604)
- **Position type for components 1-2**: Party centroids computed as mean(x), mean(y) from individual MP PCA projections (line 2747)
- **Position type for components 3-10**: Mean SVD vector per party, with component value extracted by index
- **Data source**: `svd_vectors` table filtered by `entity_type='mp'` and `window_id='current_parliament'`

## Next Steps
1. (No pending work — analysis was completed)

## Critical Context
- **For components 1 and 2**: Party positions come from `load_positions()` which performs PCA on Procrustes-aligned MP SVD vectors, then computes party centroids by averaging x/y coordinates of all MPs in that party
- **For components 3-10**: Party positions come from `load_party_axis_scores()` which computes mean SVD vector per party from `window='current_parliament'`
- **Bootstrap CIs**: Computed via `_cached_bootstrap_cis()` at `explorer.py:873-880` using `compute_party_bootstrap_cis()` from `analysis/political_axis.py`
- **MP→Party mapping**: Via `mp_metadata` table, normalized using `_PARTY_NORMALIZE` dict at `explorer.py:471-480`

## File Operations
### Read
- `/home/sgeboers/Projects/stemwijzer/explorer.py` (full file: lines 1-3094)
- `/home/sgeboers/Projects/stemwijzer/analysis/political_axis.py` (full file: lines 1-695)
- `/home/sgeboers/Projects/stemwijzer/explorer_helpers.py` (full file: lines 1-317)

### Modified
- (none)
