Complete singular collineations and quadrics

We construct wonderful compactifications of the spaces of linear maps, and symmetric linear maps of a given rank as blow-ups of secant varieties of Segre and Veronese varieties. Furthermore, we investigate their birational geometry and their relations with some spaces of degree two stable maps.
Comment: 23 pages. Exposition improved and proof of Proposition 4.1 simplified thanks to the comments of the referee. Added a section on the positivity of the anti-canonical divisor of the compactifications. arXiv admin note: text overlap with arXiv:2012.13999