{"id":122611,"date":"2008-09-29T19:14:00","date_gmt":"2008-09-29T19:14:00","guid":{"rendered":"http:\/\/www.esri.com\/arcgis-blog\/products\/product\/uncategorized\/understanding-geostatistical-analyst-layers\/"},"modified":"2008-09-29T19:14:00","modified_gmt":"2008-09-29T19:14:00","slug":"understanding-geostatistical-analyst-layers","status":"publish","type":"blog","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/product\/analytics\/understanding-geostatistical-analyst-layers","title":{"rendered":"Understanding Geostatistical Analyst Layers"},"author":5201,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"open","ping_status":"closed","template":"","format":"standard","meta":{"_acf_changed":false,"_searchwp_excluded":""},"categories":[23341],"tags":[35601,25631],"industry":[],"product":[],"class_list":["post-122611","blog","type-blog","status-publish","format-standard","hentry","category-analytics","tag-geostatistical-analyst","tag-spatial-analysis"],"acf":{"short_description":"The Geostatistical Analyst (GA for short) uses sample points taken at\ndifferent locations in a landscape and creates (interpolates) a con...","flexible_content":[{"acf_fc_layout":"content","content":"<p>The Geostatistical Analyst (GA for short) uses sample points taken at<br \/>\ndifferent locations in a landscape and creates (interpolates) a continuous surface.<br \/>\nThe sample points are measurements of some phenomenon, such as radiation leaking<br \/>\nfrom a nuclear power plant, an oil spill, or elevation heights. Geostatistical<br \/>\nAnalyst derives a surface using the values from the measured locations to predict<br \/>\nvalues for each location in the landscape.<!--more--><\/p>\n<p>The results of an analysis using GA are saved to a geostatistical layer<br \/>\n(GA layer for short), illustrated below. A GA layer is like any ArcMap layer;<br \/>\nyou add, remove, rename, and alter its symbology in countless ways.<\/p>\n<p><a href=\"http:\/\/downloads2.esri.com\/blogs\/images\/dev_2706.jpg\" target=\"_blank\"><img decoding=\"async\" src=\"http:\/\/downloads2.esri.com\/blogs\/images\/dev_2706.jpg\" alt=\"\" border=\"0\" \/><\/a><\/p>\n<p>GA layers store the source data (typically point features) and the<br \/>\nparameters used to interpolate values, but do not store the full result of the<br \/>\ninterpolation. When a GA layer is drawn in ArcMap, a coarse grid is<br \/>\nplaced over the whole extent of the layer and values are interpolated on-the-fly for each cell in the grid.<br \/>\nThese interpolated values are used to create the filled isolines displayed by<br \/>\nthe layer. These isolines are only produced for 10 classes that fall between<br \/>\nthe min and max values of the source data. The resolution of the grid is optimized so as to speed up the drawing of the<br \/>\nlayer; using a finer grid would cripple drawing speed. (Note: when deemed<br \/>\nnecessary, the drawing algorithm uses a finer resolution grid to interpolate<br \/>\nvalues in complex areas.)<\/p>\n<p>The fact that a GA layer interpolates values on-the-fly is sometimes a<br \/>\nsource of confusion. For example, when a GA layer is exported to a grid using<br \/>\nthe <a href=\"http:\/\/webhelp.esri.com\/arcgisdesktop\/9.3\/index.cfm?id=1843&amp;pid=1839&amp;topicname=GA_Layer_to_Grid_%28Geostatistical_Analyst%29\" target=\"_blank\">GA Layer to Grid<\/a> tool, interpolation is performed for each cell of the output grid. If your output<br \/>\ngrid has 1000 rows and 1000 columns, one million calculations are performed.<br \/>\n(In contrast, the grid used to draw a GA layer may be 100 rows and 100 columns).<br \/>\nFine resolution output grids may require several billion calculations.<br \/>\nObviously, the performance of the GA Layer to Grid tool depends on the<br \/>\nresolution of the output grid.<\/p>\n<p>There is another effect of exporting the layer to a grid \u2014 the output cell values, and therefore the min and max values of the output grid, can be affected by the grid&#8217;s cell size.<br \/>\nThe min and max values<br \/>\nof the grid are almost always different from the min and max values of the input<br \/>\ndata. For example, the illustration below shows a GA layer with its min and max<br \/>\nvalues and the exported grid with its min and max values. Note both the visual<br \/>\nand statistical difference between the min and max values of the two displays.<\/p>\n<p><em><a href=\"http:\/\/downloads2.esri.com\/blogs\/images\/dev_2707.jpg\" target=\"_blank\"><img decoding=\"async\" src=\"http:\/\/downloads2.esri.com\/blogs\/images\/dev_2707.jpg\" alt=\"\" border=\"0\" \/><\/a><br \/>\n<\/em><\/p>\n<p>Exact interpolators, such as Inverse Distance Weighting, can produce an output<br \/>\ngrid that has a max value that is less than the input data&#8217;s max value,<br \/>\nas illustrated above. This happens when the input point containing the max<br \/>\nvalue does not fall in the exact center of an output grid cell. In such cases,<br \/>\nthe max value is weighted according to the distance from the cell center as well<br \/>\nas nearby points.<\/p>\n<p><strong>Suggested readings<\/strong><\/p>\n<p><a href=\"http:\/\/webhelp.esri.com\/arcgisdesktop\/9.3\/index.cfm?TopicName=Understanding_geostatistical_analysis\">Understanding Geostatistical Analysis <\/a><\/p>\n<p><a href=\"http:\/\/webhelp.esri.com\/arcgisdesktop\/9.3\/index.cfm?topicname=what_is_a_geostatistical_layer?\">What is a Geostatistical Layer? <\/a><\/p>\n<p><a href=\"http:\/\/support.esri.com\/index.cfm?fa=knowledgebase.techarticles.gateway&amp;p=43&amp;pf=553\">Knowledge Base Articles<\/a><\/p>\n<p><a href=\"http:\/\/forums.esri.com\/forums.asp?c=93&amp;s=997#997\">Geostatistical Analyst Forum<\/a><\/p>\n"}],"authors":[{"ID":5201,"user_firstname":"Steve","user_lastname":"Lynch","nickname":"Steve Lynch","user_nicename":"stevelynch","display_name":"Steve Lynch","user_email":"slynch@esri.com","user_url":"","user_registered":"2018-03-02 00:16:52","user_description":"Steve Lynch is a Senior Product Engineer on the Spatial Analyst Team and has been with Esri since 2003. Previously he was a Senior Research Fellow at the University of KwaZulu-Natal in Pietermaritzburg, South Africa. His primary focus was research into long term rainfall variability and the mapping thereof.","user_avatar":"<img data-del=\"avatar\" src='https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2025\/05\/sdl_2024_600x600_300dpi-213x200.jpg' class='avatar pp-user-avatar avatar-96 photo ' height='96' width='96'\/>"}]},"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v25.9 (Yoast SEO v25.9) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Understanding Geostatistical Analyst Layers<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.esri.com\/arcgis-blog\/products\/product\/analytics\/understanding-geostatistical-analyst-layers\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Understanding Geostatistical Analyst Layers\" \/>\n<meta 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