Ratio of 1σ confidence interval relative to the 1σ value from angular galaxy clustering (D_g) for ΛCDM parameters. Constraints are marginalised over the 20 galaxy bias parameters. Plain lines are for a DESI-like survey, while dashed lines are for an Euclid-like survey. Blue line shows D_g (our reference here), orange lines show D_z, and green lines show D_g,  z. We see that for most parameters (except σ₈) confidence intervals shrink by ∼50% when using D_z instead of D_g. When using the combination D_g,  z, 1σ intervals are shrunk by at least 60% for all parameters.