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**Contents**
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[[_TOC_]]
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`NetAtmoQC` uses information about the [model domain's geometry and grid resolution](https://hirlam.org/trac/wiki/HarmonieSystemDocumentation/ModelDomain) in order to [thin the data](#using-the-domain-for-data-thinning), as well as to [reduce memory usage and improve performance](#using-the-domain-to-reduce-memory-usage-and-improve-performance).
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The default domain is "METCOOP25C", as described in the [list of Harmonie domains](https://hirlam.org/trac/browser/Harmonie/scr/Harmonie_domains.pm), but you can, of course, [specify another domain](#domain-specification) if you so wish.
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# Domain Specification
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If you wish to use a different domain, you need to add a `[domain]` section to your config file, with geometry and grid resolution parameters compatible with [those used in Harmonie](https://hirlam.org/trac/wiki/HarmonieSystemDocumentation/ModelDomain). For instance, to use the "SCANDINAVIA" domain (also defined in the [list of Harmonie domains](https://hirlam.org/trac/browser/Harmonie/scr/Harmonie_domains.pm)), you can add the following section to your config file:
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```toml
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[domain]
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name = "Scandinavia" # The name is arbitrary
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tstep = 300
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nlon = 256
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nlat = 288
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lonc = 14.0
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latc = 59.2
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lon0 = -10.0
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lat0 = 59.2
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gsize = 11000
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```
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# Using the Domain for Data Thinning
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Observations whose stations are located outside the adopted domain's area are discarded even before performing clustering. Moreover, the `select` command discards all but one observation for each point of a support grid based on the domain's original grid.
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To define the support grid used by the `select` command for the final data thinning, set, under the config file's `[commands.select]` section, the parameter `thinning_grid_coarse_factor`. This parameter should be an integer larger than zero and defines how much coarser the coarse grid is w.r.t. the original one. The default is `thinning_grid_coarse_factor=4`.
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# Using the Domain to Reduce Memory Usage and Improve Performance
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By default, NetAtmoQC divides the domain into smaller, regular subdomains and performs a preliminary clustering run on the separate subdomains before it performs the main, whole-domain clustering. The main run uses only those observations that were accepted at the pre-clustering step.
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To control how the domain is split into subdomains, add the config `split.lon` and `split.lat` to the `[domain]` section of the config file. These two parameters should be integers, larger than zero, and, respectively, divisors of `nlon` and `nlat`. The defaults are `split.lon=3` and `split.lat=4`.
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# Visualising the Configured Domain
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This can be done by running
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netatmoqc show --domain |
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