World Ecological Facets Landform Classes

Landforms are large recognizable features such as mountains, hills and plains; they are an important determinant of ecological character, habitat definition and terrain analysis. Landforms are important to the distribution of life in natural systems and are the basis for opportunities in built systems, and therefore landforms play a useful role in all natural science fields of study and planning disciplines. Dataset Summary Phenomenon Mapped: Landforms Geographic Extent: Global Projection: WGS 1984 Mosaic Projection: Web Mercator Auxiliary Sphere Units: Meters Cell Size: 231.91560581932 meters Pixel Depth: 8-bit unsigned integer Analysis: Restricted single source analysis. Maximum size of analysis is 30,000 x 30,000 pixels. Source: Esri Publication Date: May 2016 ArcGIS Server URL: https://landscape7.arcgis.com/arcgis/ In February 2017, Esri updated the World Landforms - Improved Hammond Method service with two display functions: Ecological Land Units landform classes and Ecological Facets landform classes. This layer represents Ecological Facets landform classes. You can view the Ecological Land Units landform classes by choosing Image Display, and changing the Renderer. This layer was produced using the Improved Hammond Landform Classification Algorithm produced by Esri in 2016. This algorithm published and described by Karagulle et al. 2017: Modeling global Hammond landform regions from 250-m elevation data in Transactions in GIS. The algorithm, which is based on the most recent work in this area by Morgan, J. & Lesh, A. 2005: Developing Landform Maps Using Esri’s Model Builder., Esri converted Morgan’s model into a Python script and revised it to work on global 250-meter resolution GMTED2010 elevation data. Hammond’s landform classification characterizes regions rather than identifying individual features, thus, this layer contains sixteen classes of landforms: * Nearly flat plains * Smooth plains with some local relief * Irregular plains with moderate relief * Irregular plains with low hills * Scattered moderate hills * Scattered high hills * Scattered low mountains * Scattered high mountains * Moderate hills * High hills * Tablelands with moderate relief * Tablelands with considerable relief * Tablelands with high relief * Tablelands with very high relief * Low mountains * High mountains To produce these classes, Esri staff first projected the 250-meter resolution GMTED elevation data to the World Equidistant Cylindrical coordinate system. Each cell in this dataset was assigned three characteristics: slope based on 3-km neighborhood, relief based on 6 km neighborhood, and profile based on 6-km neighborhood. The last step was to overlay the combination of these three characteristics with areas that are exclusively plains. Slope is the percentage of the 3-km neighborhood occupied by gentle slope. Hammond specified 8% as the threshold for gentle slope. Slope is used to define how flat or steep the terrain is. Slope was classified into one of four classes: ────────────────────────────────────────┬───────────── Percent of neighborhood over 8% of slope│Slope Classes ────────────────────────────────────────┼───────────── 0 - 20% │400 ────────────────────────────────────────┼───────────── 21% -50% │300 ────────────────────────────────────────┼───────────── 51% - 80% │200 ────────────────────────────────────────┼───────────── >81% │100 ────────────────────────────────────────┴───────────── Local Relief is the difference between the maximum and minimum elevation within in the 6-km neighborhood. Local relief is used to define terrain how rugged or the complexity of the terrain"s texture. Relief was assigned one of six classes: ──────────────────────┬─────────────── Change in elevation │Relief Class ID ──────────────────────┼─────────────── 0 – 30 meters │10 ──────────────────────┼─────────────── 31 meter – 90 meters │20 ──────────────────────┼─────────────── 91 meter – 150 meters │30 ──────────────────────┼─────────────── 151 meter – 300 meters│40 ──────────────────────┼─────────────── 301 meter – 900 meters│50 ──────────────────────┼─────────────── >900 meters │60 ──────────────────────┴─────────────── The combination of slope and relief begin to define terrain as mountains, hills and plains. However, the difference between mountains or hills and tablelands cannot be distinguished using only these parameters. Profile is used to determine tableland areas. Profile identifies neighborhoods with upland and lowland areas, and calculates the percent area of gently sloping terrain within those upland and lowland areas. A 6-km circular neighborhood was used to calculate the profile parameter. Upland/lowland is determined by the difference between average local relief and elevation. In the 6-km neighborhood window, if the difference between maximum elevation and cell’s elevation is smaller than half of the local relief it’s an upland. If the difference between maximum elevation and cell’s elevation is larger than half of the local relief it’s a lowland. Profile was assigned one of five classes: ────────────────────────────────────────────────────────────────┬───────────── Percent of neighborhood over 8% slope in upland or lowland areas│Profile Class ────────────────────────────────────────────────────────────────┼───────────── Less than 50% gentle slope is in upland or lowland │0 ────────────────────────────────────────────────────────────────┼───────────── More than 75% of gentle slope is in lowland │1 ────────────────────────────────────────────────────────────────┼───────────── 50%-75% of gentle slope is in lowland │2 ────────────────────────────────────────────────────────────────┼───────────── 50-75% of gentle slope is in upland │3 ────────────────────────────────────────────────────────────────┼───────────── More than 75% of gentle slope is in upland │4 ────────────────────────────────────────────────────────────────┴───────────── Early reviewers of the resulting classes noted one confusing outcome, which was that areas were classified as "plains with low mountains", or "plains with hills" were often mostly plains, and the hills or mountains were part of an adjacent set of exclusively identified hills or mountains. To address this areas that are exclusively plains were produced, and used to override these confusing areas. The hills and mountains within those areas were converted to their respective landform class. The combination of slope, relief and profile merged with the areas of plains, can be better understood using the following diagram, which uses the colors in this layer to show which classes are present and what parameter values produced them: [Hammond Classification by parameter] What can you do with this layer? This layer is suitable for both visualization and analysis. It can be used in ArcGIS Online in web maps and applications and can be used in ArcGIS Desktop. Restricted single source analysis means this layer has size constraints for analysis and it is not recommended for use with other layers in multisource analysis. This layer is part of a larger collection of [landscape layers] that you can use to perform a wide variety of mapping and analysis tasks. The [Living Atlas of the World] provides an easy way to explore the landscape layers and many other beautiful and authoritative maps on hundreds of topics. [Geonet] is a good resource for learning more about landscape layers and the Living Atlas of the World. To get started see the [Living Atlas Discussion Group]. The [Esri Insider Blog] provides an introduction to the Ecophysiographic Mapping project.