Table 3.

Variable and parameter definitions

Variable	Explanation
A, B	Area
i, j	Population
v	Layer
$\mathcal{E}$	Pool of excitatory neurons
$\mathcal{I}$	Pool of inhibitory neurons
S	Surface area
D	Cortical thickness
R	Radius of a cortical area
$R_0$	Radius of a $1{\mathrm{mm}}^2$ area
N	Number of neurons
$\mathit{\gamma }$	Fraction of excitatory neurons
$\mathit{\rho }$	Volume density of neurons
$N_{\mathrm{syn}}$	Number of synapses
${\mathit{\rho }}_{\mathrm{syn}}$	Volume density of synapses
$\mathit{\sigma }$	Spatial width of Gaussian profile underlying the intrinsic connectivity
$C_0$	Peak of Gaussian connectivity profile averaged across population pairs
$\overline{C}$	Connection probability averaged over all possible positions of two neurons
K($K^{\mathrm{out}}$)	Average indegree (outdegree) (number of synapses per target/source neuron)
$\mathcal{K}$(${\mathcal{K}}^{\mathrm{out}}$)	Relative average indegree (outdegree)
$c_A$	Area-specific conversion factor for indegrees
NLN	Number of labeled neurons (as in Markov et al. 2011)
FLN	Fraction of labeled neurons (as in Markov et al. 2011)
SLN	Fraction of supragranularly labeled neurons (as in Markov et al. 2014b)
c	Normalization constant of the decay of FLN over inter-area distance (see Eq. 10)
$\mathit{\lambda }$	Length constant of the decay of FLN over inter-area distance (see Eq. 10)
$d_{AB}$	Distance between areas A and B (see Eq. 10)
$c_{B,\mathit{\beta }}$	Overlap of area $\mathit{\beta }$ in the M132 scheme and area B in the FV91 scheme
$\mathit{\varphi }$	Dispersion parameter of the beta-binomial distribution governing the labeling of neurons in source areas
$\ell$	Log ratio of neuron densities of two areas (see Eq. 1)
$a_0,a_1$	Fit parameters of the sigmoidal SLN relation (see Eq. 1)
$c_{\mathrm{B}}$	Cell body
$s_{\mathrm{cc}}$	Cortico-cortical synapse
S	Pool of supragranular layers (i.e., layer 2/3)
I	Pool of infragranular layers (i.e., layers 5 and 6)
$P_{\mathrm{s}}$	Pattern of source layers
$P_{\mathrm{t}}$	Pattern of target layers
$\mathit{\alpha }(v)$	Qualitative connection strength for layer v from CoCoMac (see Supplementary Eq. 3)
$X_j$	Fraction of synapses formed by neurons in source population j (see Supplementary Eq. 3)
$Y_v$	Fraction of synapses formed in target layer v (see Supplementary Eq. 3)
$Z_i$	Factor for redistributing synapses to ensure the E–I specificity of cortico-cortical connections (see Supplementary Eq. 3)