diff --git a/modules/core/context.js b/modules/core/context.js
index 9427aaf6b..b9bfe958c 100644
--- a/modules/core/context.js
+++ b/modules/core/context.js
@@ -586,12 +586,19 @@ export function coreContext() {
 
 
     function loadNSIPresets() {
-      return fileFetcher.get('nsi_presets')
-        .then(d => {
+      return Promise.all([
+          fileFetcher.get('nsi_presets'),
+          fileFetcher.get('nsi_features')
+        ])
+        .then(vals => {
           // Add `suggestion=true` to all the nsi presets
           // The preset json schema doesn't include it, but the iD code still uses it
-          Object.values(d.presets).forEach(preset => preset.suggestion = true);
-          presetManager.merge({ presets: d.presets });
+          Object.values(vals[0].presets).forEach(preset => preset.suggestion = true);
+
+          presetManager.merge({
+            presets: vals[0].presets,
+            featureCollection: vals[1]
+          });
         })
         .catch(() => { /* ignore */ });
     }
diff --git a/modules/presets/index.js b/modules/presets/index.js
index 50a795955..a97ab7d0d 100644
--- a/modules/presets/index.js
+++ b/modules/presets/index.js
@@ -1,5 +1,8 @@
 import { dispatch as d3_dispatch } from 'd3-dispatch';
 
+import LocationConflation from '@ideditor/location-conflation';
+import whichPolygon from 'which-polygon';
+
 import { prefs } from '../core/preferences';
 import { fileFetcher } from '../core/file_fetcher';
 import { osmNodeGeometriesForTags, osmSetAreaKeys, osmSetPointTags, osmSetVertexTags } from '../osm/tags';
@@ -7,7 +10,7 @@ import { presetCategory } from './category';
 import { presetCollection } from './collection';
 import { presetField } from './field';
 import { presetPreset } from './preset';
-import { utilArrayUniq, utilRebind } from '../util';
+import { utilArrayChunk, utilArrayUniq, utilRebind } from '../util';
 
 export { presetCategory };
 export { presetCollection };
@@ -45,13 +48,20 @@ export function presetIndex() {
   let _fields = {};
   let _categories = {};
   let _universal = [];
+  let _customFeatures = {};
+  let _resolvedFeatures = {};     // cache of all locationSet Features
   let _addablePresetIDs = null;   // Set of preset IDs that the user can add
   let _recents;
   let _favorites;
 
+  let _deferred = new Set();
+  let _queue = [];
+
   // Index of presets by (geometry, tag key).
   let _geometryIndex = { point: {}, vertex: {}, line: {}, area: {}, relation: {} };
 
+  let _loco;
+  let _featureIndex;
   let _loadPromise;
 
   _this.ensureLoaded = () => {
@@ -77,13 +87,33 @@ export function presetIndex() {
   };
 
 
+  // `merge` accepts an object containing new preset data (all properties optional):
+  // {
+  //   fields: {},
+  //   presets: {},
+  //   categories: {},
+  //   defaults: {},
+  //   featureCollection: {}
+  //}
   _this.merge = (d) => {
+
+    // Cancel any existing deferred work - we'll end up redoing it after this merge
+    _queue = [];
+    Array.from(_deferred).forEach(handle => {
+      window.cancelIdleCallback(handle);
+      _deferred.delete(handle);
+    });
+
     // Merge Fields
     if (d.fields) {
       Object.keys(d.fields).forEach(fieldID => {
         const f = d.fields[fieldID];
         if (f) {   // add or replace
           _fields[fieldID] = presetField(fieldID, f);
+          if (!_fields[fieldID].locationSet) {
+            _fields[fieldID].locationSet = { include: ['Q2'] };  // default worldwide
+            _fields[fieldID].locationSetID = '+[Q2]';
+          }
         } else {   // remove
           delete _fields[fieldID];
         }
@@ -97,6 +127,10 @@ export function presetIndex() {
         if (p) {   // add or replace
           const isAddable = !_addablePresetIDs || _addablePresetIDs.has(presetID);
           _presets[presetID] = presetPreset(presetID, p, isAddable, _fields, _presets);
+          if (!_presets[presetID].locationSet) {
+            _presets[presetID].locationSet = { include: ['Q2'] };  // default worldwide
+            _presets[presetID].locationSetID = '+[Q2]';
+          }
         } else {   // remove (but not if it's a fallback)
           const existing = _presets[presetID];
           if (existing && !existing.isFallback()) {
@@ -155,7 +189,87 @@ export function presetIndex() {
       });
     });
 
+    // Merge Custom Features
+    if (d.featureCollection && Array.isArray(d.featureCollection.features)) {
+      d.featureCollection.features.forEach(feature => {
+        const featureID = feature.id || (feature.properties && feature.properties.id);
+        if (featureID) {   // add or replace
+          _customFeatures[featureID] = feature;
+        }
+      });
+    }
+
+    // Replace LocationConflation resolver if new customFeatures have been added
+    // (Would be nice in a future version to be able to add new custom features to it, rather than replacing entirely)
+    if (!_loco || d.featureCollection) {
+      _loco = new LocationConflation({ type: 'FeatureCollection', features: Object.values(_customFeatures) });
+      resolveLocationSet({ include: ['Q2'] });    // resolve the default "world" feature
+    }
+
+    // Resolve all features -> geojson, processing data in chunks
+    let toResolve = Object.values(_presets).concat(Object.values(_fields))
+      .filter(d => !d.locationSetID);
+
+    _queue = utilArrayChunk(toResolve, 250);
+
+    // Everything after here will be deferred.
+    processQueue()
+      .then(() => { // Rebuild feature index
+        _featureIndex = whichPolygon({ type: 'FeatureCollection', features: Object.values(_resolvedFeatures) });
+      });
+
     return _this;
+
+
+    function processQueue() {
+      if (!_queue.length) return Promise.resolve();
+
+      const chunk = _queue.pop();
+      return new Promise(resolvePromise => {
+          const handle = window.requestIdleCallback(() => {
+            _deferred.delete(handle);
+            resolveLocationSets(chunk);
+            resolvePromise();
+          });
+          _deferred.add(handle);
+        })
+        .then(() => processQueue());
+    }
+
+
+    function resolveLocationSets(items) {
+      if (!Array.isArray(items)) return;
+      items.forEach(item => {
+        let locationSet = item.locationSet || { include: ['Q2'] };  // fallback to world
+        let locationSetID;
+
+        try {
+          locationSetID = resolveLocationSet(locationSet);
+        } catch (err) {
+          locationSet = { include: ['Q2'] };  // fallback to world
+          locationSetID = '+[Q2]';
+        }
+        // store this info with the preset/field
+        item.locationSet = locationSet;
+        item.locationSetID = locationSetID;
+      });
+    }
+
+    function resolveLocationSet(locationSet) {
+      const resolved = _loco.resolveLocationSet(locationSet);
+      const locationSetID = resolved.id;
+      if (!resolved.feature.geometry.coordinates.length || !resolved.feature.properties.area) {
+        throw new Error(`locationSet ${locationSetID} resolves to an empty feature.`);
+      }
+      if (!_resolvedFeatures[locationSetID]) {  // First time seeing this locationSet feature
+        let feature = JSON.parse(JSON.stringify(resolved.feature));   // deep clone
+        feature.id = locationSetID;      // Important: always use the locationSet `id` (`+[Q30]`), not the feature `id` (`Q30`)
+        feature.properties.id = locationSetID;
+        _resolvedFeatures[locationSetID] = feature;  // insert into cache
+      }
+      return locationSetID;
+    }
+
   };