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There are many properties of soils that are available to use for analyses such as this, for example stoniness, depth to bedrock, etc. The two factors we chose are extremely important soil properties in supporting different plant communities.Landform represents where a location is with respect to elevation, slope, and aspect (direction a hillside is facing). Landform distinguishes hilltops, hill sides, valley bottoms, etc. We used the RIGIS digital terrain model as our source of elevation data to measure landform. Landform classes were identified using GIS modeling of slope, aspect, and elevation. A description of landform categories and the technical methods to obtain them can be found here.The final ELU map is made by adding together the raster datasets for landform, drainage class, and soil texture. Because we were careful with our encoding system, the sum of the three rasters provides us a composite of the individual datasets. For example, a location that is a well-drained (code value 2000) and consists of gravelly sand (code value 100) a sits on a hilltop (code value 21) and would combine to be ELU 2121 (2000+100+21). This process yielded 204 unique ELUs for the state of Rhode Island. Examination of a cumulative distribution function (CDF) of the ELUs showed that most of the ELUs were small and did not occur very often. Conversely, 20 ELUs were quite common and encompassed almost 85% of the land area of RI.", "geometryType": "esriGeometryPolygon", "sourceSpatialReference": { "wkid": 102730, "latestWkid": 3438, "xyTolerance": 0.003280833333333333, "zTolerance": 0.001, "mTolerance": 0.001, "falseX": -18120300, "falseY": -47742100, "xyUnits": 3048.0060960121928, "falseZ": 0, "zUnits": 1, "falseM": 0, "mUnits": 1 }, "copyrightText": "URI EDC, URI NRS, URI CRC, Sea Grant RI, TNC", "parentLayer": null, "subLayers": [], "minScale": 0, "maxScale": 0, "drawingInfo": { "renderer": { "type": "simple", "symbol": { "type": "esriSFS", "style": "esriSFSSolid", "color": [ 169, 0, 230, 153 ], "outline": null } }, "scaleSymbols": true, "transparency": 40, "labelingInfo": null }, "defaultVisibility": false, "extent": { "xmin": -7999205.054357148, "ymin": 5034246.930339024, "xmax": -7922500.538624678, "ymax": 5162908.417645802, "spatialReference": { "wkid": 102100, "latestWkid": 3857, "xyTolerance": 0.001, "zTolerance": 0.001, "mTolerance": 0.001, "falseX": -20037700, "falseY": -30241100, "xyUnits": 10000, "falseZ": -100000, "zUnits": 10000, "falseM": -100000, "mUnits": 10000 } }, "hasAttachments": false, "htmlPopupType": "esriServerHTMLPopupTypeAsHTMLText", "displayField": "Quality", "typeIdField": null, "subtypeFieldName": null, "subtypeField": null, "defaultSubtypeCode": null, "fields": [ { "name": "OBJECTID", "type": "esriFieldTypeOID", "alias": "OBJECTID", "domain": null }, { "name": "ID", "type": "esriFieldTypeDouble", "alias": "ID", "domain": null }, { "name": "GRIDCODE", "type": "esriFieldTypeDouble", "alias": "GRIDCODE", "domain": null }, { "name": "Acres", "type": "esriFieldTypeDouble", "alias": "Acres", "domain": null }, { "name": "Quality", "type": "esriFieldTypeString", "alias": "Quality", "length": 12, "domain": null }, { "name": "SD_Class", "type": "esriFieldTypeSmallInteger", "alias": "SD_Class", "domain": null }, { "name": "Shape", "type": "esriFieldTypeGeometry", "alias": "Shape", "domain": null }, { "name": "Shape.STArea()", "type": "esriFieldTypeDouble", "alias": "Shape.STArea()", "domain": null }, { "name": "Shape.STLength()", "type": "esriFieldTypeDouble", "alias": "Shape.STLength()", "domain": null } ], "geometryField": { "name": "Shape", "type": "esriFieldTypeGeometry", "alias": "Shape" }, "indexes": [ { "name": "R77_pk", "fields": "OBJECTID", "isAscending": true, "isUnique": true, "description": "" }, { "name": "S65_idx", "fields": "Shape", "isAscending": true, "isUnique": true, "description": "" } ], "subtypes": [], "relationships": [], "canModifyLayer": true, "canScaleSymbols": false, "hasLabels": false, "capabilities": "Query,Map,Data", "maxRecordCount": 2000, "supportsStatistics": true, "supportsAdvancedQueries": true, "supportedQueryFormats": "JSON, geoJSON, PBF", "isDataVersioned": false, "ownershipBasedAccessControlForFeatures": {"allowOthersToQuery": true}, "useStandardizedQueries": true, "advancedQueryCapabilities": { "useStandardizedQueries": true, "supportsStatistics": true, "supportsHavingClause": true, "supportsOrderBy": true, "supportsDistinct": true, "supportsCountDistinct": true, "supportsPagination": true, "supportsTrueCurve": true, "supportsReturningQueryExtent": true, "supportsQueryWithDistance": true, "supportsSqlExpression": true }, "supportsDatumTransformation": true, "dateFieldsTimeReference": null, "hasMetadata": true, "isDataArchived": false, "archivingInfo": { "supportsQueryWithHistoricMoment": false, "startArchivingMoment": -1 }, "supportsCoordinatesQuantization": true, "supportsDynamicLegends": true }