Maps of the cosmic web are usually based on the distribution of galaxies, but recently a complementary perspective has been gained by mapping the three-dimensional structure of the intergalactic medium. I will describe the Lyman-alpha Tomography IMACS Survey (LATIS), a Magellan program that has produced the largest Mpc-resolution maps of the IGM at z~2.5. The technique is based on detecting spatially and spectrally coherent Lyman-alpha absorption in the spectra of thousands of faint galaxies. The LATIS maps provide a new way to detect large-scale structures in the cosmic noon era, particularly large voids and the ancestors of galaxy clusters, that is uniquely independent of the structures' galaxy content. We aim to use these maps to address when and how galaxies' environments began to affect their evolution. I will present initial results based on the LATIS maps, focusing mainly on galaxies in protoclusters, as well as future prospects.
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