Embodiments presented herein provide techniques for creating and simplifying a cell and portal graph. The simplified cell and portal graph may be used to make a conservative determination of whether an element of geometry is visible for a given view frustum (and therefore needs to be rendered). That is, the simplified cell and portal graph retains the encoded visibility for given set of geometry. The simplified cell and portal graph provides a “conservative” determination of visibility as it may indicate that some objects are visible that are not (resulting in unneeded rendering), but not the other way around. Further, this approach allows cell and portal graphs to be generated dynamically, allowing the cell and portal graphs to be used for scenes where the geometry can change (e.g., as 3D world of a video game).