此地图由牛津大学疟疾地图集项目 (MAP)、Google、欧盟联合研究中心 (JRC) 和荷兰特温特大学合作制作。用于生成地图的基础数据集包括道路（首次在全球范围内使用 Open Street Map 和 Google 道路数据集）、铁路、河流、湖泊、海洋、地形条件（坡度和海拔）、地表覆盖类型和国界。
这些数据集均分配了以时间（即穿越相应像素类型所需的时间）表示的行驶速度。然后，将这些数据集组合起来，生成“摩擦表面”，即一种地图，其中每个像素都根据该像素内出现的类型分配了一个名义上的总体出行速度。我们结合使用最低成本路径算法（在 Google Earth Engine 中运行，对于高纬度地区，则在 R 中运行）和此摩擦表面，计算了从所有位置到最近城市（按出行时间计算）的出行时间。城市是使用全球人类住区项目创建的高密度覆盖产品确定的。
D.J. Weiss、A. Nelson, H.S. Gibson, W. Temperley, S. Peedell, A.
Lieber, M. Hancher, E. Poyart, S. Belchior, N. Fullman, B. Mappin，U. Dalrymple, J. Rozier、T.C.D. Lucas、R.E. Howes、L.S. Tusting、S.Y. Kang、E. Cameron, D. Bisanzio, K.E. Battle, S. Bhatt 和 P.W. Gething。一张显示 2015 年前往各城市所需旅行时间的全球地图，用于评估可达性方面的不平等情况。Nature（2018 年）。
doi:10.1038/nature25181
[null,null,[],[[["\u003cp\u003eThis dataset provides a global map of travel time to the nearest densely populated area, calculated for the year 2015.\u003c/p\u003e\n"],["\u003cp\u003eIt covers areas between 85 degrees north and 60 degrees south, utilizing various data sources like roads, railways, and land cover to model travel time.\u003c/p\u003e\n"],["\u003cp\u003eDensely populated areas are defined as those with 1,500 or more inhabitants per square kilometer or a built-up area with at least 50,000 inhabitants.\u003c/p\u003e\n"],["\u003cp\u003eThe dataset was produced through a collaboration between the University of Oxford Malaria Atlas Project, Google, the European Union Joint Research Centre, and the University of Twente.\u003c/p\u003e\n"],["\u003cp\u003eIt is licensed under a Creative Commons Attribution 4.0 International License.\u003c/p\u003e\n"]]],[],null,["# Accessibility to Cities 2015\n\nDataset Availability\n: 2015-01-01T00:00:00Z--2016-01-01T00:00:00Z\n\nDataset Provider\n:\n\n\n [Malaria Atlas Project](https://malariaatlas.org/research-project/accessibility-to-cities/)\n\nTags\n:\n[accessibility](/earth-engine/datasets/tags/accessibility) [jrc](/earth-engine/datasets/tags/jrc) [map](/earth-engine/datasets/tags/map) [oxford](/earth-engine/datasets/tags/oxford) [population](/earth-engine/datasets/tags/population) [twente](/earth-engine/datasets/tags/twente) \n\n#### Description\n\nThis global accessibility map enumerates land-based\ntravel time to the nearest densely-populated area for all areas\nbetween 85 degrees north and 60 degrees south for a nominal year 2015.\n\nDensely-populated areas are defined as contiguous areas\nwith 1,500 or more inhabitants per square kilometer or a majority\nof built-up land cover types coincident with a population center\nof at least 50,000 inhabitants.\n\nThis map was produced through\na collaboration between the University of Oxford Malaria Atlas\nProject (MAP), Google, the European Union Joint Research Centre\n(JRC), and the University of Twente, Netherlands. The underlying\ndatasets used to produce the map include roads (comprising the\nfirst ever global-scale use of Open Street Map and Google roads\ndatasets), railways, rivers, lakes, oceans, topographic conditions\n(slope and elevation), landcover types, and national borders.\n\nThese datasets were each allocated a speed or speeds of travel in terms\nof time to cross each pixel of that type. The datasets were then\ncombined to produce a \"friction surface\", a map where\nevery pixel is allocated a nominal overall speed of travel based\non the types occurring within that pixel. Least-cost-path algorithms\n(running in Google Earth Engine and, for high-latitude areas, in\nR) were used in conjunction with this friction surface to calculate\nthe time of travel from all locations to the nearest city (by travel\ntime). Cities were determined using the high-density-cover product\ncreated by the Global Human Settlement Project.\n\nEach pixel in the resultant accessibility map thus represents the modeled shortest\ntime from that location to a city.\n\nSource dataset credits are as described in the accompanying paper.\n\n### Bands\n\n**Bands**\n\n| Name | Units | Min | Max | Pixel Size | Description |\n|-----------------|-------|-----|-------|---------------|----------------------------------------------------|\n| `accessibility` | min | 0 | 41556 | 927.67 meters | Travel time to the nearest densely-populated area. |\n\n### Terms of Use\n\n**Terms of Use**\n\nThis work is licensed under a [Creative Commons Attribution\n4.0 International License](https://creativecommons.org/licenses/by/4.0/).\n\n### Citations\n\nCitations:\n\n- D.J. Weiss, A. Nelson, H.S. Gibson, W. Temperley, S. Peedell, A.\n Lieber, M. Hancher, E. Poyart, S. Belchior, N. Fullman, B. Mappin,\n U. Dalrymple, J. Rozier, T.C.D. Lucas, R.E. Howes, L.S. Tusting,\n S.Y. Kang, E. Cameron, D. Bisanzio, K.E. Battle, S. Bhatt, and\n P.W. Gething. A global map of travel time to cities to assess inequalities\n in accessibility in 2015. Nature (2018).\n [doi:10.1038/nature25181](https://doi.org/10.1038/nature25181)\n\n### Explore with Earth Engine\n\n| **Important:** Earth Engine is a platform for petabyte-scale scientific analysis and visualization of geospatial datasets, both for public benefit and for business and government users. Earth Engine is free to use for research, education, and nonprofit use. To get started, please [register for Earth Engine access.](https://console.cloud.google.com/earth-engine)\n\n### Code Editor (JavaScript)\n\n```javascript\nvar dataset = ee.Image('Oxford/MAP/accessibility_to_cities_2015_v1_0');\nvar accessibility = dataset.select('accessibility');\nvar accessibilityVis = {\n min: 0.0,\n max: 41556.0,\n gamma: 4.0,\n};\nMap.setCenter(18.98, 6.66, 2);\nMap.addLayer(accessibility, accessibilityVis, 'Accessibility');\n```\n[Open in Code Editor](https://code.earthengine.google.com/?scriptPath=Examples:Datasets/Oxford/Oxford_MAP_accessibility_to_cities_2015_v1_0) \n[Accessibility to Cities 2015](/earth-engine/datasets/catalog/Oxford_MAP_accessibility_to_cities_2015_v1_0) \nThis global accessibility map enumerates land-based travel time to the nearest densely-populated area for all areas between 85 degrees north and 60 degrees south for a nominal year 2015. Densely-populated areas are defined as contiguous areas with 1,500 or more inhabitants per square kilometer or a majority of built-up land ... \nOxford/MAP/accessibility_to_cities_2015_v1_0, accessibility,jrc,map,oxford,population,twente \n2015-01-01T00:00:00Z/2016-01-01T00:00:00Z \n-60 -180 85 180 \nGoogle Earth Engine \nhttps://developers.google.com/earth-engine/datasets\n\n- [](https://doi.org/https://malariaatlas.org/research-project/accessibility-to-cities/)\n- [](https://doi.org/https://developers.google.com/earth-engine/datasets/catalog/Oxford_MAP_accessibility_to_cities_2015_v1_0)"]]
