diff --git a/mapshaper.js b/mapshaper.js
index d7c450e7..0aec2c0e 100644
--- a/mapshaper.js
+++ b/mapshaper.js
@@ -25429,8 +25429,11 @@ ${svg}
       .option('no-replace', noReplaceOpt);
 
     parser.command('rectangles')
-      .describe('create a rectangle around each feature in a layer')
+      .describe('create a rectangle for each feature in a layer')
       .option('offset', offsetOpt)
+      .option('bbox', {
+        describe: 'Use an expression to generate a rectangle for each feature'
+      })
       .option('aspect-ratio', aspectRatioOpt)
       .option('name', nameOpt)
       .option('target', targetOpt)
@@ -38806,18 +38809,20 @@ ${svg}
 
   // Create rectangles around each feature in a layer
   cmd.rectangles = function(targetLyr, targetDataset, opts) {
-    if (!layerHasGeometry(targetLyr)) {
-      stop("Layer is missing geometric shapes");
-    }
     var crsInfo = getDatasetCrsInfo(targetDataset);
     var records = targetLyr.data ? targetLyr.data.getRecords() : null;
-    var geometries = targetLyr.shapes.map(function(shp) {
-      var bounds = targetLyr.geometry_type == 'point' ?
-        getPointFeatureBounds(shp) : targetDataset.arcs.getMultiShapeBounds(shp);
-      bounds = applyRectangleOptions(bounds, crsInfo.crs, opts);
-      if (!bounds) return null;
-      return bboxToPolygon(bounds.toArray(), opts);
-    });
+    var geometries;
+
+    if (opts.bbox) {
+      geometries = bboxExpressionToGeometries(opts.bbox, targetLyr, targetDataset);
+
+    } else {
+      if (!layerHasGeometry(targetLyr)) {
+        stop("Layer is missing geometric shapes");
+      }
+      geometries = shapesToBoxGeometries(targetLyr, targetDataset, opts);
+    }
+
     var geojson = {
       type: 'FeatureCollection',
       features: geometries.map(function(geom, i) {
@@ -38839,6 +38844,39 @@ ${svg}
     return outputLayers;
   };
 
+  function shapesToBoxGeometries(lyr, dataset, opts) {
+    var crsInfo = getDatasetCrsInfo(dataset);
+    return lyr.shapes.map(function(shp) {
+      var bounds = lyr.geometry_type == 'point' ?
+        getPointFeatureBounds(shp) : dataset.arcs.getMultiShapeBounds(shp);
+      bounds = applyRectangleOptions(bounds, crsInfo.crs, opts);
+      if (!bounds) return null;
+      return bboxToPolygon(bounds.toArray(), opts);
+    });
+  }
+
+  function bboxExpressionToGeometries(exp, lyr, dataset, opts) {
+    var compiled = compileFeatureExpression(exp, lyr, dataset.arcs, {});
+    var n = getFeatureCount(lyr);
+    var result;
+    var geometries = [];
+    for (var i=0; i<n; i++) {
+      result = compiled(i);
+      if (!looksLikeBbox(result)) {
+        stop('Invalid bbox value (expected a GeoJSON-type bbox):', result);
+      }
+      geometries.push(bboxToPolygon(result));
+    }
+    return geometries;
+  }
+
+  function looksLikeBbox(o) {
+    if (!o || o.length != 4) return false;
+    if (o.some(isNaN)) return false;
+    if (o[0] <= o[2] == false || o[1] <= o[3] == false) return false;
+    return true;
+  }
+
   // Create rectangles around one or more target layers
   //
   cmd.rectangle2 = function(target, opts) {
@@ -45536,7 +45574,7 @@ ${svg}
     });
   }
 
-  var version = "0.6.84";
+  var version = "0.6.85";
 
   // Parse command line args into commands and run them
   // Function takes an optional Node-style callback. A Promise is returned if no callback is given.