diff --git a/gis/LeafletDataSet.js b/gis/LeafletDataSet.js
index ad801c8f..b468c9c9 100644
--- a/gis/LeafletDataSet.js
+++ b/gis/LeafletDataSet.js
@@ -1,6 +1,7 @@
 // import * as TileData from './TileData.js'
 import * as util from '../src/utils.js'
 import * as gis from '../src/gis.js'
+import GeoDataSet from '../src/GeoDataSet.js'
 // import RGBDataSet from './RGBDataSet.js'
 
 class LeafletDataSet {
@@ -91,8 +92,8 @@ class LeafletDataSet {
         const dataSetMatrix = this.dataSetsMatrix(tilesBBox, z)
         const tilesDataSet = this.dataSetMatrixToDataSet(dataSetMatrix)
         const cropParameters = this.getCropParameters(bbox, z)
-        const bboxDataSet = tilesDataSet.crop(cropParameters)
-        bboxDataSet.bbox = bbox
+        const croppedDataSet = tilesDataSet.crop(cropParameters)
+        const bboxDataSet = GeoDataSet.viewFromDataSet(croppedDataSet, bbox)
 
         console.log('bbox', bbox)
         console.log('tilesBBox', tilesBBox)
diff --git a/models/DropletsModel.js b/models/DropletsModel.js
index 529d0bce..2bf9763f 100644
--- a/models/DropletsModel.js
+++ b/models/DropletsModel.js
@@ -15,7 +15,7 @@ export default class DropletsModel extends Model {
     //    'patchAspect',
     //    'dataSetAspectNearest',
     //    'dataSetAspectBilinear',
-    stepType = 'minNeighbor'
+    stepType = 'dataSetAspectNearest'
     moves // how many moves in a step
     // Installed datasets:
     elevation
diff --git a/models/scripts/DropletsModel.js b/models/scripts/DropletsModel.js
index 84d3544e..ab1d79d5 100644
--- a/models/scripts/DropletsModel.js
+++ b/models/scripts/DropletsModel.js
@@ -15,7 +15,7 @@ class DropletsModel extends Model {
     //    'patchAspect',
     //    'dataSetAspectNearest',
     //    'dataSetAspectBilinear',
-    stepType = 'minNeighbor'
+    stepType = 'dataSetAspectNearest'
     moves // how many moves in a step
     // Installed datasets:
     elevation
diff --git a/src/AS.js b/src/AS.js
index 0942a43e..66543f48 100644
--- a/src/AS.js
+++ b/src/AS.js
@@ -52,3 +52,5 @@ export { default as Mouse } from './Mouse.js'
 export * as gis from './gis.js'
 export * as geojson from './geojson.js'
 export { default as GeoWorld } from './GeoWorld.js'
+export { default as GeoDataSet } from './GeoDataSet.js'
+
diff --git a/src/AS0.js b/src/AS0.js
index 11762c9b..34dc72d0 100644
--- a/src/AS0.js
+++ b/src/AS0.js
@@ -52,3 +52,4 @@ export { default as Mouse } from './Mouse.js'
 export * as gis from './gis.js'
 export * as geojson from './geojson.js'
 export { default as GeoWorld } from './GeoWorld.js'
+export { default as GeoDataSet } from './GeoDataSet.js'
diff --git a/src/GeoDataSet.js b/src/GeoDataSet.js
new file mode 100644
index 00000000..ee686b97
--- /dev/null
+++ b/src/GeoDataSet.js
@@ -0,0 +1,182 @@
+import DataSet from "./DataSet.js"
+import { bboxMetricSize } from './gis.js'
+class GeoDataSet extends DataSet {
+
+    /**
+     * Mostly the same a DataSet except it has bounds. 
+     * A few methods, like slope, dzdx, dzdy, and aspect are different because they take into account the size of the bbox in meters
+     * 
+     * @param {Number} width width of the DataSet in pixels
+     * @param {Number} height height of the DataSet in pixels
+     * @param {Array} bbox [west, south, east, north]
+     * @param {TypedArray} data 
+     */
+    constructor(width, height, bbox, data) {
+        super(width, height, data)
+        this.bbox = bbox
+    }
+
+    /**
+     * Create a view of a Dataset including the bounds. 
+     * 
+     * @static
+     * @param {DataSet} dataSet 
+     * @param {Array} bbox [west, south, east, north]
+     * @returns {GeoDataSet} GeoDataSet view of the dataset data. It is a view not a copy. 
+     */
+    static viewFromDataSet(dataSet, bbox) {
+        return new GeoDataSet(dataSet.width, dataSet.height, bbox, dataSet.data)
+    }
+
+    lat2y(lat) {
+        const [west, south, east, north] = this.bbox
+        const y = Math.round(this.height * (lat - south) / (north - south))
+        return y
+    }
+
+    lon2x(lng) {
+        const [west, south, east, north] = this.bbox
+        const x = Math.round(this.width * (lng - west) / (east - west))
+        return x
+    }
+
+    // Convert from geoon/lat coords to pixel coords
+    toPixel(geoX, geoY) {
+        return [this.lon2x(geoX), this.lat2y(geoY)]
+    }
+
+    // Get pixel from geo lon/lat coords to pixel coords
+    getGeo(geoX, geoY) {
+        const [x, y] = this.toPixel(geoX, geoY)
+        return this.getXY(x, y)
+    }
+
+    // Set pixel from geo lon/lat coords to pixel coords
+    // I think this could be a slow way to set data for large amounts
+    setGeo(geoX, geoY, value) {
+        const [x, y] = this.toPixel(geoX, geoY)
+        return this.setXY(x, y, value)
+    }
+
+    /**
+     * Samples a pixel at a given latitude and longitude
+     * 
+     * @param {Number} geoX longitude
+     * @param {Number} geoY latitude
+     * @param {Boolean} useNearest 
+     * @throws Out Of Range Error - when it is outside of the bbox
+     * @returns {Number}
+     */
+    sampleGeo(geoX, geoY, useNearest = true) {
+        const [x, y] = this.toPixel(geoX, geoY)
+        return this.sample(x, y, useNearest)
+    }
+
+    /**
+     * Change in z value in terms of x. Finite difference.
+     * 
+     * @returns {GeoDataset}
+     */
+    dzdx() {
+        const [widthMeters, heightMeters] = bboxMetricSize(this.bbox)
+        const pixelScale = widthMeters / this.width
+        const dzdx = super.dzdx(2, (1 / 8) * (1 / pixelScale)) // (1/8) for the kernel and 1/pixelscale to get units right
+        const dzdx2 = GeoDataSet.viewFromDataSet(dzdx, this.bbox)
+        return dzdx2
+    }
+
+    /**
+     * Change in z value in terms of y. Finite difference.
+     * 
+     * @returns {GeoDataSet}
+     */
+    dzdy() {
+        const [widthMeters, heightMeters] = bboxMetricSize(this.bbox)
+        const pixelScale = heightMeters / this.height
+        const dzdy = super.dzdy(2, (1 / 8) * (1 / pixelScale))
+        const dzdy2 = GeoDataSet.viewFromDataSet(dzdy, this.bbox)
+        return dzdy2
+    }
+
+    /**
+     * Create dzdx, dzdy, slope, and aspect in one function. 
+     * 
+     * @returns {SlopeAndAspect} {dzdx, dzdy, slope, aspect}  
+     */
+    slopeAndAspect() {
+        const dzdx = this.dzdx()
+        const dzdy = this.dzdy()
+        const slope = this.slope(dzdx, dzdy)
+        const aspect = this.aspect(dzdx, dzdy)
+        return { dzdx, dzdy, slope, aspect }
+    }
+
+    /**
+     * The aspect of each pixel in radians.
+     * 
+     * @param {GeoDataset} dzdx 
+     * @param {GeoDataSet} dzdy 
+     * @returns {GeoDataSet} Aspect in radians.
+     */
+    aspect(dzdx = this.dzdx(), dzdy = this.dzdy()) {
+        const asp = dzdx.map((x, i) => {
+            const y = dzdy.data[i]
+            const a = Math.atan2(-y, -x)
+            return a
+        })
+        return asp
+    }
+
+    /**
+     * Returns the slope in radians
+     * 
+     * @param {GeoDataset} dzdx 
+     * @param {GeoDataset} dzdy 
+     * @returns {GeoDataset}
+     */
+    slope(dzdx = this.dzdx(), dzdy = this.dzdy()) {
+        const slop = dzdx.map((x, i) => {
+            const y = dzdy.data[i]
+            const a = Math.hypot(-x, -y)
+            const sl = (Math.PI / 2) - Math.atan2(1, a)
+            return sl
+        })
+        return slop
+    }
+
+    //
+    // The functions below are the same as DataSet's version except they return a GeoDataset instead of a dataset.
+    // Is there a better way to do this?
+    //
+    //
+    clone() {
+        return new GeoDataSet(this.width, this.height, this.bbox, this.data)
+    }
+
+    resample(width, height, useNearest = true, Type = Array) {
+        const a = super.resample(width, height, useNearest, Type)
+        const b = GeoDataSet.viewFromDataSet(a, this.bbox)
+        return b
+    }
+
+    convolve(kernel, factor = 1, crop = false) {
+        const a = super.convolve(kernel, factor, crop)
+        const b = GeoDataSet.viewFromDataSet(a, this.bbox)
+        return b
+    }
+
+    normalize(lo = 0, hi = 1, round = false) {
+        const a = super.normalize(lo, hi, round)
+        const b = GeoDataSet.viewFromDataSet(a, this.bbox)
+        return b
+    }
+
+    map(f) {
+        const a = super.map(f)
+        const b = GeoDataSet.viewFromDataSet(a, this.bbox)
+        return b
+    }
+}
+
+export default GeoDataSet
+
diff --git a/src/TileData.js b/src/TileData.js
index 7e11bb0c..b2925043 100644
--- a/src/TileData.js
+++ b/src/TileData.js
@@ -1,5 +1,7 @@
 import * as util from './utils.js'
 import RGBDataSet from './RGBDataSet.js'
+import GeoDataSet from './GeoDataSet.js'
+import {xyz2bbox} from './gis.js'
 
 // ============= rgb to elevation/numeric =============
 
@@ -28,7 +30,9 @@ const sharedTileObject = {
     },
     zxyToDataSet: async function (z, x, y, ArrayType = Float32Array) {
         const img = await this.zxyToTile(z, x, y)
-        return this.tileDataSet(img, ArrayType)
+        const ds1 = this.tileDataSet(img, ArrayType)
+        const bbox = xyz2bbox(x, y, z)
+        return GeoDataSet.viewFromDataSet(ds1, bbox)
     },
     tileDataSet: function (img, ArrayType = Float32Array) {
         const tileDecoder = this.elevationFcn
diff --git a/test/samples.txt b/test/samples.txt
index 9ee2a4f4..9419e240 100644
--- a/test/samples.txt
+++ b/test/samples.txt
@@ -2,7 +2,7 @@
   "ants": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"population\",\"speed\",\"maxPheromone\",\"diffusionRate\",\"evaporationRate\",\"wiggleAngle\",\"foodX\",\"foodY\",\"nestX\",\"nestY\"],\"patches\":6561,\"patch\":{\"id\":4174,\"isFood\":false,\"isNest\":false,\"foodPheromone\":0.0257680536425004,\"nestPheromone\":0.04021862087665316,\"_diffuseNext\":0,\"neighbors\":[4092,4093,4094,4175,4256,4255,4254,4173]},\"turtles\":255,\"turtle\":{\"id\":80,\"theta\":0.35187919106928417,\"x\":4.569458552541104,\"y\":1.1474232505464783,\"carryingFood\":true,\"pheromone\":0.37713422825070403},\"links\":0}",
   "buttons": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"population\",\"cluster\",\"done\"],\"patches\":1089,\"patch\":{\"id\":273},\"turtles\":200,\"turtle\":{\"id\":136,\"theta\":2.283142302887487,\"x\":-10,\"y\":-16,\"links\":[112,150,412,438]},\"links\":500,\"link\":{\"id\":482,\"end0\":{\"id\":121,\"theta\":3.7783750618803937,\"x\":10,\"y\":9,\"links\":[194,200,482,484]},\"end1\":{\"id\":192,\"theta\":5.1900867760030405,\"x\":-15,\"y\":-8,\"links\":[77,274,366,454,482,499]}}}",
   "diffuse": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"population\",\"speed\",\"wiggleAngle\",\"radius\",\"diffuseRate\",\"seedDelta\",\"seedMax\"],\"patches\":80601,\"patch\":{\"id\":45451,\"ran\":0.6014832474734432,\"_diffuseNext\":0,\"neighbors\":[45049,45050,45051,45452,45853,45852,45851,45450]},\"turtles\":2,\"turtle\":{\"id\":1,\"theta\":4.017593726538558,\"x\":-169.46259631353462,\"y\":-13.334433990431691},\"links\":0}",
-  "droplets": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"speed\",\"stepType\",\"moves\",\"elevation\",\"dzdx\",\"dzdy\",\"slope\",\"aspect\",\"localMins\"],\"patches\":10201,\"patch\":{\"id\":5057,\"elevation\":1723.09375,\"aspect\":4.24928055747772,\"neighbors\":[4955,4956,4957,5058,5159,5158,5157,5056],\"isLocalMin\":false},\"turtles\":10201,\"turtle\":{\"id\":7694,\"theta\":0.6867621740671395,\"x\":-29.91422888528167,\"y\":-19.749582869876278,\"done\":true},\"links\":0}",
+  "droplets": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"speed\",\"stepType\",\"moves\",\"elevation\",\"dzdx\",\"dzdy\",\"slope\",\"aspect\",\"localMins\"],\"patches\":10201,\"patch\":{\"id\":5057,\"elevation\":1723.09375,\"aspect\":4.24928055747772,\"neighbors\":[4955,4956,4957,5058,5159,5158,5157,5056],\"isLocalMin\":false},\"turtles\":9584,\"turtle\":{\"id\":7632,\"theta\":1.4478503085133343,\"x\":5.4447649576110795,\"y\":-24.843932317600657,\"done\":true},\"links\":0}",
   "exit": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"numExits\",\"population\",\"exits\",\"inside\",\"wall\"],\"patches\":5041,\"patch\":{\"id\":4012,\"neighbors4\":[3941,4013,4083,4011],\"turtles\":[],\"neighbors\":[3940,3941,3942,4013,4084,4083,4082,4011]},\"turtles\":9,\"turtle\":{\"id\":1039,\"theta\":-0.7853981633974483,\"x\":15,\"y\":-22,\"exit\":{\"id\":4313,\"exitNumber\":0,\"turtles\":[]}},\"links\":0}",
   "fire": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"density\",\"fires\",\"embers\",\"patchTypes\",\"dirtType\",\"treeType\",\"fireType\",\"burnedTrees\",\"initialTrees\"],\"patches\":63001,\"patch\":{\"id\":52543,\"type\":\"ember0\",\"neighbors4\":[52292,52544,52794,52542]},\"turtles\":0,\"links\":0}",
   "flock": "{\"ticks\":500,\"model\":[\"world\",\"patches\",\"turtles\",\"links\",\"ticks\",\"step0\",\"step\",\"toRads\",\"fromRads\",\"toAngleRads\",\"fromAngleRads\",\"toCCW\",\"population\",\"vision\",\"speed\",\"maxTurn\",\"minSeparation\"],\"patches\":1089,\"patch\":{\"id\":901,\"turtles\":[]},\"turtles\":100,\"turtle\":{\"id\":62,\"theta\":8.580787915677849,\"x\":-0.5027269158976337,\"y\":-6.08771206064941},\"links\":0}",
diff --git a/views3d/avalanche.html b/views3d/avalanche.html
new file mode 100644
index 00000000..f20589f2
--- /dev/null
+++ b/views3d/avalanche.html
@@ -0,0 +1,135 @@
+<html>
+
+<head>
+    <title>Avalanche</title>
+    <link rel="icon" type="image/x-icon" href="../favicon.ico" />
+</head>
+
+<body>
+    <script type="module">
+        import * as util from '../src/utils.js'
+        import World from '../src/World.js'
+        import Model from '../src/Model.js'
+        import { mapzen as provider } from '../src/TileData.js'
+
+        import TwoDraw from '../src/TwoDraw.js'
+        import Animator from '../src/Animator.js'
+        import Color from '../src/Color.js'
+        import ColorMap from '../src/ColorMap.js'
+        import DataSet from '../src/DataSet.js'
+        import GeoDataSet from '../src/GeoDataSet.js'
+        import { xyz2bbox, bboxMetricSize } from '../src/gis.js'
+        import ThreeDraw from '../src/ThreeDraw.js'
+
+        const pi = Math.PI
+        /**
+         * 
+         * Model
+         * 
+         * **/
+        export default class AvalancheModel extends Model {
+            // ======================
+            constructor(worldOptions = World.defaultOptions(50)) {
+                super(worldOptions)
+            }
+
+            // data can be gis zxy or a DataSet
+            async startup() {
+                const z = 13, x = 1555, y = 3084
+                const bounds = xyz2bbox(x, y, z)// alta utah. USA
+                const elev = await provider.zxyToDataSet(z, x, y)
+                this.installDataSets(elev)
+            }
+
+            installDataSets(elevation) {
+                const { slope, aspect, dzdx, dzdy } = elevation.slopeAndAspect()
+                this.patches.importDataSet(aspect, 'aspect')
+                this.patches.importDataSet(slope, 'slope')
+                this.patches.importDataSet(dzdx, 'dzdx')
+                this.patches.importDataSet(dzdy, 'dzdy')
+                this.patches.importDataSet(elevation, 'elevation')
+                // for 3d 
+                const elevationScaled = elevation.clone().scale(-10, 10)
+                this.patches.importDataSet(elevationScaled, 'z', true) // for drawing
+            }
+            setup() {
+                this.patches.ask(p => {
+                    p.snowDepth = 1
+                })
+            }
+            step() {
+                // start new buffer
+                this.patches.ask(p => p.nextSnow = p.snowDepth)
+                // drop snow
+                this.patches.ask(p => p.nextSnow += + 0.01)
+                // make avalanche
+                this.patches.ask(p => {
+                    const maxSnowDepth = (pi) / (p.slope)
+                    if (p.snowDepth > maxSnowDepth) {
+                        //choose the 2 downhill neighbors to give snow to
+                        const n = Math.min(2, p.neighbors.length)
+                        p.neighbors.minNOf(n, 'elevation')
+                            .ask(p2 => p2.nextSnow = p2.nextSnow + p.snowDepth / n)
+                        p.nextSnow = 0
+                    }
+                })
+                // swap buffer
+                this.patches.ask(p => p.snowDepth = p.nextSnow)
+            }
+        }
+
+
+        /**
+         * 
+         * View
+         * 
+         * */
+        const snowColor = ColorMap.gradientColorMap(20, ['rgb(98,52,18)', 'white'])
+        const drawOptions = {
+            patchesMesh: 'PointsMesh',
+            patchesSize: 4,
+            patchesColor: p => {
+                const aspect2 = (p.aspect + 2*pi) % (2*pi)
+                const k = (pi - Math.abs(aspect2 - pi))/pi
+                const snow = snowColor.scaleColor(p.snowDepth, 0, 6)
+                const col = Color.typedColor(k * snow[0], k * snow[1], k * snow[2])
+                return col
+            },
+        }
+
+        const model = new AvalancheModel()
+        await model.startup()
+        model.setup()
+
+         const view = new ThreeDraw(
+            model,
+            { div: 'modelDiv' },
+            drawOptions
+        )
+
+        // const view = new TwoDraw(
+        //     model,
+        //     {
+        //         div: 'modelDiv',
+        //         patchSize: 4,
+        //         useSprites: true, // lots of turtles, sprites faster
+        //     },
+        //     drawOptions
+        // )
+
+        const anim = new Animator(
+            () => {
+                model.step()
+                view.draw()
+            },
+            400, // run 500 steps
+            30 // 30 fps
+        )
+
+        util.toWindow({ util, model, view, anim, ColorMap, Color })
+
+    </script>
+    <div id="modelDiv"></div>
+</body>
+
+</html>
\ No newline at end of file