diff --git a/src/main.ts b/src/main.ts
index 93e0dd9..02747d7 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,6 +1,6 @@
 import './style/main.css';
 import { initMap } from './map/map-init.js';
-import { HexOverlayLayer } from './map/hex-layer.js';
+import { createHexLayer } from './map/hex-layer.js';
 import { attachHexInteraction, type HexClickEvent } from './map/hex-interaction.js';
 import { HexMap } from '../core/hex-map.js';
 import type { AxialCoord, TerrainType } from '../core/types.js';
@@ -15,23 +15,23 @@ import {
   enforceEdgeConstraints,
   applyConstraintActions,
 } from '../core/edge-connectivity.js';
-import * as api from './data/api-client.js';
+
+const STORAGE_KEY = 'hexifyer_map';
 
 // --- State ---
 const hexMap = new HexMap();
 let currentMode: ToolMode = 'select';
 let selectedTerrain: TerrainType | null = null;
 let selectedHex: AxialCoord | null = null;
-let hexSize = 48;
+const hexSize = 48; // Fixed per map — set once
 const origin = { x: 0, y: 0 };
-let currentMapId: number | null = null;
 let saveTimeout: ReturnType<typeof setTimeout> | null = null;
 
 // --- Init Map ---
 const map = initMap('map');
 
 // --- Hex Layer ---
-let hexLayer = new HexOverlayLayer({
+const hexLayer = createHexLayer({
   hexSize,
   hexMap,
   origin,
@@ -44,63 +44,83 @@ hexLayer.addTo(map);
 const sidebarEl = document.getElementById('sidebar')!;
 const { toolbar, terrainPicker, hexInspector, settings } = createSidebar(sidebarEl);
 
+const terrainPickerUI = createTerrainPicker(terrainPicker, (terrain) => {
+  selectedTerrain = terrain;
+});
+
 createToolbar(toolbar, (mode) => {
   currentMode = mode;
   terrainPickerUI.setMode(mode);
 });
 
-const terrainPickerUI = createTerrainPicker(terrainPicker, (terrain) => {
-  selectedTerrain = terrain;
-});
-
 const hexInspectorUI = createHexInspector(hexInspector);
 
-createMapSettings(settings, { hexSize, showGrid: true, opacity: 0.7 }, (s) => {
-  if (s.hexSize !== hexSize) {
-    hexSize = s.hexSize;
-    rebuildHexLayer(s.showGrid, s.opacity);
-  } else {
-    hexLayer.setShowGrid(s.showGrid);
-    hexLayer.setHexOpacity(s.opacity);
-  }
+createMapSettings(settings, { showGrid: true, opacity: 0.7 }, (s) => {
+  hexLayer.setShowGrid(s.showGrid);
+  hexLayer.setHexOpacity(s.opacity);
 });
 
-// --- Rebuild hex layer (when hex size changes) ---
-function rebuildHexLayer(showGrid: boolean, opacity: number) {
-  map.removeLayer(hexLayer);
-  hexLayer = new HexOverlayLayer({
-    hexSize,
-    hexMap,
-    origin,
-    showGrid,
-    opacity,
-  });
-  hexLayer.addTo(map);
-  reattachInteraction();
-}
-
-// --- Auto-save (debounced) ---
+// --- Auto-save to localStorage (debounced) ---
 function scheduleSave() {
-  if (!currentMapId) return;
   if (saveTimeout) clearTimeout(saveTimeout);
-  saveTimeout = setTimeout(async () => {
-    if (!currentMapId || !hexMap.dirty) return;
+  saveTimeout = setTimeout(() => {
+    if (!hexMap.dirty) return;
     try {
       const data = hexMap.serialize();
-      await api.saveHexes(currentMapId, data.hexes.map(h => ({
-        q: h.q,
-        r: h.r,
-        base: h.base,
-        features: h.features.map(f => ({ terrainId: f.terrainId, edgeMask: f.edgeMask })),
-      })));
+      localStorage.setItem(STORAGE_KEY, JSON.stringify(data));
       hexMap.markClean();
-      console.log(`[save] Saved ${data.hexes.length} hexes`);
     } catch (err) {
-      console.error('[save] Failed:', err);
+      console.error('[save] localStorage failed:', err);
     }
-  }, 1000);
+  }, 500);
 }
 
+// --- File export/import ---
+function exportMap() {
+  const data = hexMap.serialize();
+  const json = JSON.stringify(data, null, 2);
+  const blob = new Blob([json], { type: 'application/json' });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = 'hexmap.json';
+  a.click();
+  URL.revokeObjectURL(url);
+}
+
+function importMap() {
+  const input = document.createElement('input');
+  input.type = 'file';
+  input.accept = '.json';
+  input.addEventListener('change', () => {
+    const file = input.files?.[0];
+    if (!file) return;
+    const reader = new FileReader();
+    reader.onload = () => {
+      try {
+        const data = JSON.parse(reader.result as string);
+        hexMap.clear();
+        for (const hex of data.hexes) {
+          hexMap.setTerrain({ q: hex.q, r: hex.r }, {
+            base: hex.base,
+            features: hex.features,
+          });
+        }
+        hexMap.markClean();
+        hexLayer.redraw();
+        scheduleSave();
+      } catch (err) {
+        console.error('[import] Failed:', err);
+      }
+    };
+    reader.readAsText(file);
+  });
+  input.click();
+}
+
+// Expose to sidebar buttons
+(window as any).__hexifyer = { exportMap, importMap };
+
 // --- Interaction handlers ---
 
 function handleSelect(event: HexClickEvent) {
@@ -142,54 +162,33 @@ function handleFeature(event: HexClickEvent) {
 }
 
 // --- Hex Interaction ---
-let detachInteraction: (() => void) | null = null;
+attachHexInteraction(
+  map, hexSize, origin,
+  (event) => {
+    if (currentMode === 'select') handleSelect(event);
+    else if (currentMode === 'paint') handlePaint(event);
+    else if (currentMode === 'feature') handleFeature(event);
+  },
+  (event) => {
+    if (currentMode === 'paint') handlePaint(event);
+  },
+);
 
-function reattachInteraction() {
-  detachInteraction?.();
-  detachInteraction = attachHexInteraction(
-    map, hexSize, origin,
-    (event) => {
-      if (currentMode === 'select') handleSelect(event);
-      else if (currentMode === 'paint') handlePaint(event);
-      else if (currentMode === 'feature') handleFeature(event);
-    },
-    (event) => {
-      if (currentMode === 'paint') handlePaint(event);
-    },
-  );
-}
-
-reattachInteraction();
-
-// --- Load or create map from API ---
-async function init() {
-  try {
-    const maps = await api.listMaps();
-    if (maps.length > 0) {
-      currentMapId = maps[0].id;
-      console.log(`[init] Loading map "${maps[0].name}" (id: ${currentMapId})`);
-    } else {
-      const result = await api.createMap({ name: 'Default Map' });
-      currentMapId = result.id;
-      console.log(`[init] Created new map (id: ${currentMapId})`);
+// --- Load from localStorage ---
+try {
+  const saved = localStorage.getItem(STORAGE_KEY);
+  if (saved) {
+    const data = JSON.parse(saved);
+    for (const hex of data.hexes) {
+      hexMap.setTerrain({ q: hex.q, r: hex.r }, {
+        base: hex.base,
+        features: hex.features,
+      });
     }
-
-    // Load existing hexes
-    const hexes = await api.loadHexes(currentMapId);
-    if (hexes.length > 0) {
-      for (const hex of hexes) {
-        hexMap.setTerrain({ q: hex.q, r: hex.r }, {
-          base: hex.base,
-          features: hex.features,
-        });
-      }
-      hexMap.markClean();
-      hexLayer.redraw();
-      console.log(`[init] Loaded ${hexes.length} hexes`);
-    }
-  } catch (err) {
-    console.warn('[init] API not available, running without persistence:', err);
+    hexMap.markClean();
+    hexLayer.redraw();
+    console.log(`[init] Loaded ${data.hexes.length} hexes from localStorage`);
   }
+} catch (err) {
+  console.warn('[init] Failed to load from localStorage:', err);
 }
-
-init();
diff --git a/src/map/hex-layer.ts b/src/map/hex-layer.ts
index fb5ff0e..829d3b8 100644
--- a/src/map/hex-layer.ts
+++ b/src/map/hex-layer.ts
@@ -5,7 +5,7 @@ import { getHexesInBounds, type PixelBounds } from '../../core/hex-grid.js';
 import type { HexMap } from '../../core/hex-map.js';
 import { renderHex } from '../svg/renderer.js';
 
-export interface HexLayerOptions extends L.GridLayerOptions {
+export interface HexLayerOptions {
   hexSize: number;
   hexMap: HexMap;
   origin?: { x: number; y: number };
@@ -16,84 +16,88 @@ export interface HexLayerOptions extends L.GridLayerOptions {
 
 /**
  * Leaflet GridLayer that renders the hex overlay using Canvas.
- * Delegates all hex rendering to svg/renderer.ts.
+ * Uses L.GridLayer.extend() for compatibility with Leaflet's class system.
  */
-export class HexOverlayLayer extends L.GridLayer {
-  private hexSize: number;
-  private hexMap: HexMap;
-  private origin: { x: number; y: number };
-  private _selectedHex: AxialCoord | null = null;
-  private _showGrid = true;
-  private _hexOpacity = 0.7;
+export function createHexLayer(options: HexLayerOptions): L.GridLayer & {
+  setSelectedHex: (coord: AxialCoord | null) => void;
+  setShowGrid: (show: boolean) => void;
+  setHexOpacity: (opacity: number) => void;
+} {
+  let hexSize = options.hexSize;
+  let hexMap = options.hexMap;
+  const origin = options.origin ?? { x: 0, y: 0 };
+  let selectedHex: AxialCoord | null = options.selectedHex ?? null;
+  let showGrid = options.showGrid ?? true;
+  let hexOpacity = options.opacity ?? 0.7;
 
-  constructor(options: HexLayerOptions) {
-    super(options);
-    this.hexSize = options.hexSize;
-    this.hexMap = options.hexMap;
-    this.origin = options.origin ?? { x: 0, y: 0 };
-    this._selectedHex = options.selectedHex ?? null;
-    this._showGrid = options.showGrid ?? true;
-    this._hexOpacity = options.opacity ?? 0.7;
-  }
+  const HexLayer = L.GridLayer.extend({
+    createTile(coords: L.Coords): HTMLCanvasElement {
+      const canvas = document.createElement('canvas');
+      const tileSize = this.getTileSize();
+      canvas.width = tileSize.x;
+      canvas.height = tileSize.y;
+      const ctx = canvas.getContext('2d')!;
 
-  setSelectedHex(coord: AxialCoord | null): void {
-    this._selectedHex = coord;
-    this.redraw();
-  }
+      const nwPoint = coords.scaleBy(tileSize);
+      const sePoint = nwPoint.add(tileSize);
 
-  setShowGrid(show: boolean): void {
-    this._showGrid = show;
-    this.redraw();
-  }
+      const zoom = coords.z;
+      const maxZoom = this._map?.getMaxZoom() ?? 6;
+      const scale = Math.pow(2, maxZoom - zoom);
 
-  setHexOpacity(opacity: number): void {
-    this._hexOpacity = opacity;
-    this.redraw();
-  }
+      const bounds: PixelBounds = {
+        minX: nwPoint.x * scale,
+        minY: nwPoint.y * scale,
+        maxX: sePoint.x * scale,
+        maxY: sePoint.y * scale,
+      };
 
-  createTile(coords: L.Coords): HTMLCanvasElement {
-    const canvas = document.createElement('canvas');
-    const tileSize = this.getTileSize();
-    canvas.width = tileSize.x;
-    canvas.height = tileSize.y;
-    const ctx = canvas.getContext('2d')!;
+      const hexCoords = getHexesInBounds(bounds, hexSize, origin);
 
-    const nwPoint = coords.scaleBy(tileSize);
-    const sePoint = nwPoint.add(tileSize);
+      for (const coord of hexCoords) {
+        const terrain = hexMap.getTerrain(coord);
+        const pixelCenter = axialToPixel(coord, hexSize, origin);
 
-    const zoom = coords.z;
-    const maxZoom = this._map?.getMaxZoom() ?? 6;
-    const scale = Math.pow(2, maxZoom - zoom);
+        const localX = (pixelCenter.x - bounds.minX) / scale;
+        const localY = (pixelCenter.y - bounds.minY) / scale;
+        const localSize = hexSize / scale;
 
-    const bounds: PixelBounds = {
-      minX: nwPoint.x * scale,
-      minY: nwPoint.y * scale,
-      maxX: sePoint.x * scale,
-      maxY: sePoint.y * scale,
-    };
+        const geom = computeHexGeometry(localX, localY, localSize);
+        const isSelected = selectedHex !== null &&
+          selectedHex.q === coord.q &&
+          selectedHex.r === coord.r;
 
-    const hexCoords = getHexesInBounds(bounds, this.hexSize, this.origin);
+        renderHex(ctx, geom, terrain, {
+          opacity: hexOpacity,
+          showGrid,
+          selected: isSelected,
+        });
+      }
 
-    for (const coord of hexCoords) {
-      const terrain = this.hexMap.getTerrain(coord);
-      const pixelCenter = axialToPixel(coord, this.hexSize, this.origin);
+      return canvas;
+    },
+  });
 
-      const localX = (pixelCenter.x - bounds.minX) / scale;
-      const localY = (pixelCenter.y - bounds.minY) / scale;
-      const localSize = this.hexSize / scale;
+  const layer = new HexLayer() as L.GridLayer & {
+    setSelectedHex: (coord: AxialCoord | null) => void;
+    setShowGrid: (show: boolean) => void;
+    setHexOpacity: (opacity: number) => void;
+  };
 
-      const geom = computeHexGeometry(localX, localY, localSize);
-      const isSelected = this._selectedHex !== null &&
-        this._selectedHex.q === coord.q &&
-        this._selectedHex.r === coord.r;
+  layer.setSelectedHex = (coord: AxialCoord | null) => {
+    selectedHex = coord;
+    layer.redraw();
+  };
 
-      renderHex(ctx, geom, terrain, {
-        opacity: this._hexOpacity,
-        showGrid: this._showGrid,
-        selected: isSelected,
-      });
-    }
+  layer.setShowGrid = (show: boolean) => {
+    showGrid = show;
+    layer.redraw();
+  };
 
-    return canvas;
-  }
+  layer.setHexOpacity = (opacity: number) => {
+    hexOpacity = opacity;
+    layer.redraw();
+  };
+
+  return layer;
 }
diff --git a/src/svg/renderer.ts b/src/svg/renderer.ts
index ff647e0..0b6e115 100644
--- a/src/svg/renderer.ts
+++ b/src/svg/renderer.ts
@@ -255,7 +255,7 @@ function drawLinearFeature(
   const { cx, cy, edgeMidpoints, vertices } = geom;
 
   if (terrainId === 'coastline') {
-    drawCoastline(ctx, vertices, edges, color, size);
+    drawCoastlineFeature(ctx, geom, edges, size);
     return;
   }
 
@@ -374,41 +374,131 @@ function drawBezierRoute(
   ctx.stroke();
 }
 
-function drawCoastline(
+/**
+ * Coastline: routes edge-to-edge like road/river, but fills one side with water.
+ * The water side is the side AWAY from the hex center (the "outside" of the curve).
+ * We determine this using a cross-product test on the bezier midpoint.
+ */
+function drawCoastlineFeature(
   ctx: CanvasRenderingContext2D,
-  vertices: PixelCoord[],
+  geom: HexGeometry,
   edges: HexEdge[],
-  color: string,
   size: number,
 ): void {
-  ctx.strokeStyle = color;
-  ctx.lineWidth = Math.max(2, size / 5);
-  ctx.lineCap = 'round';
-  ctx.setLineDash([]);
+  const { cx, cy, edgeMidpoints, vertices } = geom;
+  const pairs = pairEdges(edges);
+  const waterColor = '#2a5574';
+  const coastColor = '#1a4a6a';
 
-  // Coastline runs along hex edges between vertices
-  // Edge i runs from vertex i to vertex (i+1)%6
-  // But our edges are reordered — we need the vertex indices for each HexEdge
-  // HexEdge NE(0)=vertex pair [5,0], E(1)=[0,1], SE(2)=[1,2],
-  // SW(3)=[2,3], W(4)=[3,4], NW(5)=[4,5]
-  const edgeToVertices: Record<HexEdge, [number, number]> = {
-    [HexEdge.NE]: [5, 0],
-    [HexEdge.E]: [0, 1],
-    [HexEdge.SE]: [1, 2],
-    [HexEdge.SW]: [2, 3],
-    [HexEdge.W]: [3, 4],
-    [HexEdge.NW]: [4, 5],
-  };
+  ctx.save();
+  clipToHex(ctx, geom);
 
-  for (const edge of edges) {
-    const [vi1, vi2] = edgeToVertices[edge];
-    const v1 = vertices[vi1];
-    const v2 = vertices[vi2];
-    ctx.beginPath();
-    ctx.moveTo(v1.x, v1.y);
-    ctx.lineTo(v2.x, v2.y);
-    ctx.stroke();
+  for (const pair of pairs) {
+    if (pair.length === 2) {
+      const p1 = edgeMidpoints[pair[0]];
+      const p2 = edgeMidpoints[pair[1]];
+
+      // Control point for the quadratic bezier (through center)
+      const cp = { x: cx, y: cy };
+
+      // Determine which side of the curve is "away" from center
+      // Sample the bezier midpoint, then offset perpendicular
+      const bezMidX = 0.25 * p1.x + 0.5 * cp.x + 0.25 * p2.x;
+      const bezMidY = 0.25 * p1.y + 0.5 * cp.y + 0.25 * p2.y;
+
+      // Tangent at midpoint (derivative of quadratic bezier at t=0.5)
+      const tanX = (p2.x - p1.x);
+      const tanY = (p2.y - p1.y);
+
+      // Perpendicular (rotated 90° CW)
+      const perpX = tanY;
+      const perpY = -tanX;
+
+      // The "water side" offset: we pick the side that is FARTHER from center
+      const testX = bezMidX + perpX * 0.1;
+      const testY = bezMidY + perpY * 0.1;
+      const distFromCenter = Math.hypot(testX - cx, testY - cy);
+      const distOther = Math.hypot(bezMidX - perpX * 0.1 - cx, bezMidY - perpY * 0.1 - cy);
+
+      const waterSide = distFromCenter > distOther ? 1 : -1;
+
+      // Fill the water side: build a path from the curve to the hex boundary on that side
+      ctx.beginPath();
+      ctx.moveTo(p1.x, p1.y);
+      ctx.quadraticCurveTo(cp.x, cp.y, p2.x, p2.y);
+
+      // Walk hex vertices on the water side from p2's edge to p1's edge
+      const waterVerts = getVerticesOnSide(pair[0], pair[1], waterSide, vertices);
+      for (const v of waterVerts) {
+        ctx.lineTo(v.x, v.y);
+      }
+      ctx.closePath();
+      ctx.fillStyle = waterColor;
+      ctx.globalAlpha = 0.6;
+      ctx.fill();
+      ctx.globalAlpha = 1;
+
+      // Draw the coastline stroke
+      ctx.beginPath();
+      ctx.moveTo(p1.x, p1.y);
+      ctx.quadraticCurveTo(cp.x, cp.y, p2.x, p2.y);
+      ctx.strokeStyle = coastColor;
+      ctx.lineWidth = Math.max(1.5, size / 10);
+      ctx.stroke();
+    } else {
+      // Dead-end: just draw as a line to center
+      const mp = edgeMidpoints[pair[0]];
+      ctx.beginPath();
+      ctx.moveTo(mp.x, mp.y);
+      ctx.lineTo(cx, cy);
+      ctx.strokeStyle = coastColor;
+      ctx.lineWidth = Math.max(1.5, size / 10);
+      ctx.stroke();
+    }
   }
+
+  ctx.restore();
+}
+
+/**
+ * Get hex vertices on one side of a coastline running from edge1 to edge2.
+ * side: 1 = clockwise from edge2 to edge1, -1 = counter-clockwise.
+ * Returns vertices between the two edge midpoints, walking around the hex boundary.
+ */
+function getVerticesOnSide(
+  edge1: HexEdge,
+  edge2: HexEdge,
+  side: number,
+  vertices: PixelCoord[],
+): PixelCoord[] {
+  // Map HexEdge to the vertex AFTER the edge midpoint (clockwise)
+  // Edge NE(0) midpoint is between vertex 5 and 0 → next vertex CW = 0
+  // Edge E(1) → 1, SE(2) → 2, SW(3) → 3, W(4) → 4, NW(5) → 5
+  const edgeToNextVertex = [0, 1, 2, 3, 4, 5];
+
+  const result: PixelCoord[] = [];
+  const startVertIdx = edgeToNextVertex[edge2];
+  const endVertIdx = (edgeToNextVertex[edge1] + 5) % 6; // vertex BEFORE edge1's midpoint
+
+  if (side > 0) {
+    // Walk clockwise from edge2's next vertex to edge1's previous vertex
+    let idx = startVertIdx;
+    for (let i = 0; i < 6; i++) {
+      result.push(vertices[idx]);
+      if (idx === endVertIdx) break;
+      idx = (idx + 1) % 6;
+    }
+  } else {
+    // Walk counter-clockwise
+    let idx = (startVertIdx + 5) % 6;
+    for (let i = 0; i < 6; i++) {
+      result.push(vertices[idx]);
+      if (idx === (endVertIdx + 1) % 6) break;
+      idx = (idx + 5) % 6;
+    }
+  }
+
+  return result;
 }
 
 // --- Main render function ---
diff --git a/src/ui/map-settings.ts b/src/ui/map-settings.ts
index a279a10..b8f70b5 100644
--- a/src/ui/map-settings.ts
+++ b/src/ui/map-settings.ts
@@ -1,5 +1,4 @@
 export interface MapSettings {
-  hexSize: number;
   showGrid: boolean;
   opacity: number;
 }
@@ -14,22 +13,6 @@ export function createMapSettings(
   function render() {
     container.innerHTML = '';
 
-    // Hex size
-    const sizeRow = document.createElement('div');
-    sizeRow.className = 'setting-row';
-    sizeRow.innerHTML = `<label>Hex size (px)</label>`;
-    const sizeInput = document.createElement('input');
-    sizeInput.type = 'number';
-    sizeInput.min = '8';
-    sizeInput.max = '256';
-    sizeInput.value = String(settings.hexSize);
-    sizeInput.addEventListener('change', () => {
-      settings.hexSize = Math.max(8, Math.min(256, Number(sizeInput.value)));
-      onChange(settings);
-    });
-    sizeRow.appendChild(sizeInput);
-    container.appendChild(sizeRow);
-
     // Show grid
     const gridRow = document.createElement('div');
     gridRow.className = 'setting-row';
diff --git a/src/ui/sidebar.ts b/src/ui/sidebar.ts
index 3875d75..0c9e263 100644
--- a/src/ui/sidebar.ts
+++ b/src/ui/sidebar.ts
@@ -34,10 +34,30 @@ export function createSidebar(container: HTMLElement): {
   settings.id = 'settings';
   settingsSection.appendChild(settings);
 
+  // File operations
+  const fileSection = document.createElement('div');
+  fileSection.className = 'sidebar-section';
+  fileSection.innerHTML = '<h3>File</h3>';
+  const fileButtons = document.createElement('div');
+  fileButtons.className = 'toolbar';
+
+  const exportBtn = document.createElement('button');
+  exportBtn.textContent = 'Export';
+  exportBtn.addEventListener('click', () => (window as any).__hexifyer?.exportMap());
+
+  const importBtn = document.createElement('button');
+  importBtn.textContent = 'Import';
+  importBtn.addEventListener('click', () => (window as any).__hexifyer?.importMap());
+
+  fileButtons.appendChild(exportBtn);
+  fileButtons.appendChild(importBtn);
+  fileSection.appendChild(fileButtons);
+
   container.appendChild(toolbarSection);
   container.appendChild(terrainSection);
   container.appendChild(inspectorSection);
   container.appendChild(settingsSection);
+  container.appendChild(fileSection);
 
   return { toolbar, terrainPicker, hexInspector, settings };
 }