Illustration by Mike Shibao, based on imagery from CMMAP.

HarvestChoice uses a so-called meso-scale spatial grid typically at 10km or 5-arc minute resolution.

 

Arc-minute?

Many of spatial datasets that HarvestChoice is generating are based on grids (we sometimes call it "meso-scale") at three different resolutions - 60 arc-minute (1 degree), 30 arc-minute (0.5 degree), and 5 arc-minute (0.08333333333... degree). We will spare the definition of arc-minute here. For convenience we often call the 5 and 30 arc-minute grids as 10km and 50km grids, respectively (although that's not exactly/technically true - since the size of grid cell changes as latitude). However, how exactly big is one cell at 5 arc-minute resolution?

Feel It Yourself

To help you understand how big (or small) a grid cell is at each spatial resolution, use the Droppr app below - showing the three resolutions of grids over global land area. The marker (Droppr) will show some information on the ground as well as the Cell ID's (we call this HCID; this is the key to retrieve spatially explicit data from our database) at each resolution. Feel free to move the Droppr around; even try it for your backyard!

  • Black cells: 60 arc-minute (1 degree) grids.
  • Blue cells: 30 arc-minute (0.5 degree) grids. Note that black lines overlaid on top of blue lines.
  • Pink cells: 5 arc-minute (0.083333.... degree) grids. Often called as 10 km grids.

Implication

For the raster-based data layers (counterpart of raster is vectors, such as country-level datasets), the resolution indicates to the unit area of same value. For climate dataset as an example, 5 arc-minute resolution means you will get a same value within the cell; no more finer information. Would that be detail enough? It often depends on the research question and analysts' capacity as much as the data availability. For regional scale studies too-high resolution data might overwhelm analysis and interpretation of results, while too-coarse resolution data would disregard spatial variability of biophysical information. There is no magic single resolution that serves all purposes; however HarvestChoice found a sweet spot at 5 arc-minute (which is also one of the most commonly used resolutions in datasets in similar disciplines). Whenever possible, upcoming spatial data products from HarvestChoice will be standardized at 5 arc-minute resolution, including the HarvestChoice DataTiles.

Citation

HarvestChoice, 2011. "How Big is One 5 Arc-Minute Grid Cell?." International Food Policy Research Institute, Washington, DC., and University of Minnesota, St. Paul, MN. Available online at http://harvestchoice.org/node/1428.

Feb 11, 2011