Detail of Central Riga with Visibility Data from the Freedom Monument

In the experimental map below, I converted the elevation map of Latvia which is a raster map into a vector map with contour lines for each five meters of elevation.  I magnifiied the central area as well.  The yellow areas are those areas that are visible from the top of the Freedom Monument according to the GRASS 6.4.l analysis done before.  A closer look will reveal that those yellow areas seem to be of higher elevations and they are "nested" showing that those areas are hills.  Since many of areas have contour lines that are far apart, except for near the river, we could say that the terrain of Riga is relatively flat?  In the map, railroad lines are shown in red, major roads in black and contour lines in green.  The distance between contour line is 5 meters of elevation.