The growth and develoopment of Semarang city has implied decreasing open space area into built up area. Even though, a sustuinable development's concept has become the main concept of Local Development Program since 2002, there are problems concerning the management of The Green Open Space (the RTH, Ruang Terbuka Hijau) in this city. The problems, for example, are the lack of optimazation of RTH especially quantitatively, prior to land conversion. The high spatial resolution of satellite image, IKONOS and Quickbird, can be used as tools to monitor the change of land conversion. Objective of this research is to calculate spread and progress of RTH conversion from RTH to housing areas from 2003 to 2007, also to predict RTH conversion for 2010.Tembalang Sub District (Kecamatan Tembalang) has been chosen as a study area which will be compared with Banyumanik, Gunung Pati, and Mijen Sub District. Analysis method is Hansen Gravity Model or Land Potential Model. The model is used to determine potential development of Tembalang Sub District. The primary factors in Hansen Gravity Model analysis are Accessibility Index and Holding Capacity. Accessibility Index is use to measure interest in an area and easiness to access the area. Holding Capacity is used to calculate spaces where house can be built.The research shows RTH for year 2003 was 2,736.84 ha for year 2007, so RTH decreased 248.11 ha (9.07%). Conversion of RTH to housing area is 73.43 ha (29.59%), 165.44 ha or 66.68% for open space, 4.63 ha (1.87%) for others, and 4.61 ha (1.86%) still as RTH. Development of Tembalang Sub District is faster than Compared sub districts (Banyumanik, Gunung Pati and Mijen), which indicated from highest attractiveness value (124.46), so until 2010. RTH's conversion to housing areas will be no less than 29.58 ha.