  In this paper, we explore the relationship between the width of a qubit
lattice constrained in one dimension and physical thresholds for scalable,
fault-tolerant quantum computation. To circumvent the traditionally low
thresholds of small fixed-width arrays, we deliberately engineer an error bias
at the lowest level of encoding using the surface code. We then address this
engineered bias at a higher level of encoding using a lattice-surgery surface
code bus that exploits this bias, or a repetition code to make logical qubits
with unbiased errors out of biased surface code qubits. Arbitrarily low error
rates can then be reached by further concatenating with other codes, such as
Steane [[7,1,3]] code and the [[15,7,3]] CSS code. This enables a scalable
fixed-width quantum computing architecture on a square qubit lattice that is
only 19 qubits wide, given physical qubits with an error rate of $8.0\times
10^{-4}$. This potentially eases engineering issues in systems with fine qubit
pitches, such as quantum dots in silicon or gallium arsenide.
