diff --git a/apps/web/components/atlas/pos-group.ts b/apps/web/components/atlas/pos-group.ts
new file mode 100644
index 0000000..2fc2d3c
--- /dev/null
+++ b/apps/web/components/atlas/pos-group.ts
@@ -0,0 +1,58 @@
+// Coarse POS bucket for the atlas's grouped layout. The atlas's POS
+// strings come from kiri (Japanese tags like 動詞, 形容詞) and jmdict
+// (English tags like "noun, common"), so this collapses both into a
+// stable five-bucket alphabet that the hierarchical squarifier can
+// pivot on.
+
+export type AtlasPosGroup =
+  | "verb"
+  | "adjective"
+  | "noun"
+  | "particle"
+  | "adverb"
+  | "other"
+
+const VERB_PATTERNS = [/動詞/, /\bv-/i, /\bv\b/i, /verb/i]
+const ADJ_PATTERNS = [/形容詞/, /形状詞/, /adjective/i, /\badj\b/i]
+const NOUN_PATTERNS = [/名詞/, /代名詞/, /\bnoun\b/i, /pronoun/i, /\bpron\b/i]
+const PARTICLE_PATTERNS = [
+  /助詞/,
+  /助動詞/,
+  /particle/i,
+  /copula/i,
+  /\bcop\b/i,
+  /auxiliary/i,
+  /\baux\b/i,
+]
+const ADVERB_PATTERNS = [/副詞/, /adverb/i, /\badv\b/i]
+
+export function posGroup(pos: string): AtlasPosGroup {
+  if (!pos) return "other"
+  if (VERB_PATTERNS.some((re) => re.test(pos))) return "verb"
+  if (ADJ_PATTERNS.some((re) => re.test(pos))) return "adjective"
+  if (NOUN_PATTERNS.some((re) => re.test(pos))) return "noun"
+  if (PARTICLE_PATTERNS.some((re) => re.test(pos))) return "particle"
+  if (ADVERB_PATTERNS.some((re) => re.test(pos))) return "adverb"
+  return "other"
+}
+
+export const POS_GROUP_LABEL: Record<AtlasPosGroup, string> = {
+  verb: "V",
+  adjective: "ADJ",
+  noun: "N",
+  particle: "PART",
+  adverb: "ADV",
+  other: "—",
+}
+
+// Render order — puts the dense buckets first so they tend to land in
+// the wider rows. squarify itself sorts by weight, so this is an
+// aesthetic-stable secondary key only.
+export const POS_GROUP_ORDER: AtlasPosGroup[] = [
+  "noun",
+  "verb",
+  "adjective",
+  "adverb",
+  "particle",
+  "other",
+]
diff --git a/apps/web/components/atlas/types.ts b/apps/web/components/atlas/types.ts
new file mode 100644
index 0000000..d81a958
--- /dev/null
+++ b/apps/web/components/atlas/types.ts
@@ -0,0 +1,5 @@
+import type { AtlasEntry } from "@yominoki/db/queries/treemap"
+import type { Laid } from "@/lib/squarify"
+
+export type LaidAtlasEntry = Laid<AtlasEntry & { weight: number }>
+export type { AtlasEntry }
diff --git a/apps/web/lib/server/atlas.ts b/apps/web/lib/server/atlas.ts
new file mode 100644
index 0000000..0471c67
--- /dev/null
+++ b/apps/web/lib/server/atlas.ts
@@ -0,0 +1,9 @@
+import { listAtlas, type AtlasEntry } from "@yominoki/db/queries/treemap"
+import { getOps } from "@/lib/db"
+
+export async function getAtlas(
+  userId: string,
+  level: 1 | 2 | 3 | 4 | 5
+): Promise<AtlasEntry[]> {
+  return listAtlas(getOps(), userId, level)
+}