Chicago-based advertising transactional services provider Strata projects that ad spending will increase between 3% and 5% in 2013. The new projection is in line with forecasts made in December by some holding company-owned media shops. Publicis Groupe’s ZenithOptimedia for example estimated that U.S. ad spending this year would climb 3.5% to nearly $166.5 billion, while WPP’s GroupM forecasted a 2.7% hike in expenditures. Strata, which is owned by Comcast Cable, processes around $50 billion in ad transactions through its software annually. The company said that based on orders placed so far for the first quarter, demand is up slightly in the home improvement and auto ad categories.