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We prove that for all integers 2≤m≤d−1, there exists doubling measures on ℝd with full support that are m-rectifiable and purely (m−1)-unrectifiable in the sense of Federer (i.e. without assuming μ≪m). The corresponding result for 1-rectifiable measures is originally due to Garnett, Killip, and Schul (2010). Our construction of higher-dimensional Lipschitz images is informed by a simple observation about square packing in the plane: N axis-parallel squares of side length s pack inside of a square of side length ⌈N1/2⌉s. The approach is robust and when combined with standard metric geometry techniques allows for constructions in complete Ahlfors regular metric spaces. One consequence of the main theorem is that for each m∈{2,3,4} and s0, f(E) has Hausdorff dimension s, and μ(f(E))>0. This is striking, because m(f(E))=0 for every Lipschitz map f:E⊂ℝm→ℍ1 by a theorem of Ambrosio and Kirchheim (2000). Another application of the square packing construction is that every compact metric space 𝕏 of Assouad dimension strictly less than m is a Lipschitz image of a compact set E⊂[0,1]m. Of independent interest, we record the existence of doubling measures on complete Ahlfors regular metric spaces with prescribed lower and upper Hausdorff and packing dimensions. 

We study the quantitative properties of Lipschitz mappings from Euclidean spaces into metric spaces. We prove that it is always possible to decompose the domain of such a mapping into pieces on which the mapping “behaves like a projection mapping” along with a “garbage set” that isarbitrarily smallin an appropriate sense. Moreover, our control is quantitative, i.e., independent of both the particular mapping and the metric space it maps into. This improves a theorem of Azzam-Schul from the paper “Hard Sard”, and answers a question left open in that paper. The proof uses ideas of quantitative differentiation, as well as a detailed study of how to supplement Lipschitz mappings by additional coordinates to form bi-Lipschitz mappings. 

We give a simple quantitative condition, involving the “mapping content” of Azzam–Schul, which implies that a Lipschitz map from a Euclidean space to a metric space must be close to factoring through a tree. Using results of Azzam–Schul and the present authors, this gives simple checkable conditions for a Lipschitz map to have a large piece of its domain on which it behaves like an orthogonal projection. The proof involves new lower bounds and continuity statements for mapping content, and relies on a “qualitative” version of the main theorem recently proven by Esmayli–Hajłasz.