Why do we have a catechism? GDC 121 answers the question with three points: ecclesial communion, a reference work, textbook and guidebook for other catechisms. Let’s read, then discuss:
121. The Prologue to the Catechism of the Catholic Church states its purpose: “This catechism aims at presenting an organic synthesis of the essential and fundamental contents of Catholic doctrine, as regards both faith and morals, in the light of the Second Vatican Council and the whole of the Church’s Tradition”. (Catechism 11) The Magisterium of the Church intends to render an ecclesial service for our times with the Catechism of the Catholic Church, recognizing that it is:
– “a valid and legitimate instrument for ecclesial communion”: (Fidei Depositum 4a; cf. Fidei Depositum 4b) it desires to promote the bond of unity in the faith by helping the disciples of Jesus Christ to make “the profession of one faith received from the Apostles”; (Catechism 815)
– “a sure norm for teaching the faith”: (Fidei Depositum 4a; cf. Fidei Depositum 4c) the Catechism of the Catholic Church offers a clear response to the legitimate right of all the baptized to know from the Church what she has received and what she believes; it is thus an obligatory point of reference for catechesis and for the other forms of the ministry of the word.
– “a sure and authentic reference text for teaching Catholic doctrine and particularly for preparing local catechisms”: (Fidei Depositum 1f; cf. Fidei Depositum 4c) the Catechism of the Catholic Church, in fact, “is not intended to replace the local catechism (duly approved)” (Fidei Depositum 4d) but “to encourage and assist in the writing of new local catechisms which take into account various situations and cultures, while carefully preserving the unity of faith and fidelity to Catholic doctrine”. (Fidei Depositum 4d)
The nature or character proper to this document of the Magisterium consists in the fact that it is a comprehensive synthesis of the faith and thus it is of universal value. In this, it differs from other documents of the Magisterium, which do not set out to present such a synthesis. It differs also from local Catechisms, which, within the context of ecclesial communion, are destined for the service of a particular portion of the people of God.
The most famous of the local catechisms in the American memory is the Baltimore Catechism. The one most in the news today is YouCat. That should place those three books in perspective.
Any comments?
Catholic Sensibility 
I’m not quite sure that the YouCat fits on the level of a ‘local catechism.’ It’s much more of an international synthesis for a particular age group. The first thing that comes to mind for a local catechism written in light of the CCC would be the U.S. Catholic Catechism for Adults. I don’t know if there are plans for developing any other local catechisms for the U.S. for other age groups. I would guess that such efforts might even fall flat, given our cultural tendency to give more weight to what comes from Rome/the international level, such as the Compendium and YouCat.
GDC 93 alludes to catechisms based not only on culture but “circumstances.” And while GDC 110 speaks also of catechisms based on “culture,” I’d say that Western Catholic youth have a fairly large area of intersect. Not a nation, but certainly a culture.
I’d suggest that a “synthesis” is an apt way of describing derivative catechisms. Anything that presents in more detail would really be a more theological treatment, more useful for theologians and ministry professionals.