You are here

How to use the snapshot comparison tool?

The snapshot comparison tool displays up to 4 different plots on the same page, allowing to compare sources, species, layers and plot types from different dates without having to open multiple browser windows.

WARNING! This page was made for computer engineering and scientific purposes, which means that despite how the standard browsing system behaves this tool could fetch unexisting data and return dummy plots more often than you would expect. Check out the minilog section for more info. It has also been reported that this tool could be slower on old computers.


The page features 4 "views" that are numbered from 0 to 3. The view 0 (top-left) is the reference, while view 1 (top-right), 2 (bottom-left) and 3 (bottom-right) are linked to the reference by a locker mechanism (see below). To enhance the display speed it is possible to toggle a view by ticking the appropriate box in the status bar.

The status bar

This is the small horizontal banner that is located on the top of screen, its features might come handy in many situation.


  • Clicking the macc logo will take you back to the index
  • The dropdown menu allows you to zoom in/out on the displayed plots
  • You can uncheck the boxes to disable some plots and improve the rendering speed

  • The permalink allows you to record the current view; simply right-click on it and select "Copy link location" to copy the link to the clipboard.
  • The minilog tracks the operations of plot loading (for more info check the description below)

The lockers

The lockers allows you to easily switch multiple values at a time by locking some parameters on the reference plot at view 0.

  • A red locker ( locked ) means that the selected field of the form is locked: its value will automatically changes as the main plot changes too.
  • A green locker ( locked ) means that the selected field is free: you're still able to modify its value anytime you want.

To switch between lockers states you'll have to click on the locker itself.

WARNING! If a locker is set on an unavailable value (for instance if species are locked and doesn't exist for the selected source), this will return a dummy plot. Check out the minilog to get more info on this.

The date locker

The date locker has a special behavior. When you first lock the date, the hours dropdown will automatically switch to the main plot value but you'll still be able to change it's value. Also note that the and buttons won't change the auxiliary plot hours, but the and buttons will.

The minilog

The minilog keeps tracks of the last 25 actions that have been done since you first loaded the page, each action being depicted as a line of text in the minilog. A minilog entry always follows the same pattern :
[Time][View][Status] Description

  • Time : The local time when the action was executed
  • View : The concerned plot view (from 0 to 3)
  • Status : The status of the request
  • Description : A short description of the request

ERROR & UNAVAILABLE : What's the difference ?

There are two majors reason to display a dummy plot. If all the parameters you entered are right (if the chosen source actually plots those) but that, for some reason, the plot hasn't been created at the date you entered, you might get an [UNAVAILABLE] statement.
On the other hand if the parameters don't stick together you'll get an [ERROR] statement. There are several types of errors :
  • time (...) out of range! : This occurs when the given date and hour is out of the range of valid times for this series of plots.
  • (...) is not available at this layer! : This occurs when the given species at the given source is not available for the selected level.
  • (...) is not available for this source! : This occurs when the given species is not available for the given source.

Known issues

  • In some rare cases, a locked plot view might not reload correctly. To fix it, you can toggle the concerned view off and on (with the checkboxes in the statusbar).
  • Depending on the browser and the network bandwidth, a relatively long delay may be observed before the plots are drawn on the screen.