Installing GDAL on CentOS?

ELGIS requires EPEL (see https://fedoraproject.org/wiki/EPEL/FAQ#howtouse for EPEL).

However I'm not sure that you really want to use ELGIS 6 on CentOS 7. Its intended for RHEL 6 / CentOS 6 / Scientific Linux 6.

Instead, you probably just want to use EPEL for CentOS 7 for something like GDAL. EPEL 7 has GDAL 1.11.0, which isn't quite the latest, but is certainly more current than the 1.9.2 that are you trying to install.