retablo

I'm still talking about maps, charts, portulan charts, etc.

I have the following text:

Sus portadas, frontispicios o cartelas son exponentes simbólicos del concepto geográfico-artístico, a modo de retablo informativo, que predominaba en cada época de impresión del mapa.

My attempt:
Their covers, frontispieces or title blocks are symbolic models of the geographic-artistic concept, as an informative billboard, that predominated at every time of impression of the map.

It is evident that billboard doesn't suit, but I don't know what to use here.

No me siento muy seguro si esta oración habla de un mapa especial o los mapas en general. Supongo cartelas refiere a los símbolos en escudos de armas, y retablo, disculpe, pero pienso showcase es la idea.

Their covers, frontispieces or insignias are symbolic explanations of the geographic-artistic concept, a kind of informative showcase that predominated in every era the map was printed.

O …in every era maps were printed.