there are specific locations on the drosophila chromosomes where transgenes are often inserted. Here is a visual map as a reference for which attp site is on which chromosome.
references
Knapp, J.-M., Chung, P., & Simpson, J. H. (2015). Generating Customized Transgene Landing Sites and Multi-Transgene Arrays in Drosophila Using phiC31 Integrase. Genetics, 199(4), 919–934. https://doi.org/10.1534/genetics.114.173187