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Here is the takeoff performance chart of the Airbus A220 (CS100). According to Wikipedia, the MTOW runway length needed is 1500 metres. However, this chart seems to suggest that a runway length of almost 2500 metres would be required for an A220-100 operating at MTOW weight.
Am I reading the chart incorrectly?
I believe that you are correctly reading the chart, however, I think you are reading the wrong chart. The chart in your question appears to be the chart for ISA +15C and for the lower performing engines (1519G), which would result in a takeoff distance of about 2500 meters (about 8200 feet). I'm posting below what I believe to be the full chart in your question from the Airport Planning Guide linked in your question - See the first image below:
The second image below shows the chart for the higher performing engines (1524G) at ISA, and would result in a takeoff distance of slightly more than 1500 Meters (about 5100 feet).
Also, as you can see from the specification sheet (last image below), the 1525G engines can provide up to 5% more thrust (reducing the takeoff distance probably to the 4800 feet shown in specification sheet). But there is not a takeoff performance chart for this engine in the Airport Planning Guide you have linked in your question.
The last image below is the specification data sheet from footnote #252 shown on the Wikipedia page you have linked in your question.
Lastly, it seems likely that the published takeoff performance shown in the Wikipedia page and the specification sheet linked as footnote #252 from the Wikipedia page, would use the most optimal circumstances to illustrate the best performance available for the CS100/A220-100. This would be at ISA using the most powerful engines (1525G).
Performance is all dependent upon aircraft gross takeoff weight, runway conditions (e.g. surface type, gradient, etc.), ambient winds and density altitude at the airfield. There is no one required length of runway needed to depart. That all has to be calculated prior to departure, and ensure that the runway available can accommodate the airplane.
Assuming the data above is correct for the purposes in question, I would start from the horizontal axis, then draw a vertical line up from the aircraft’s gross takeoff weight to the pressure altitude at the airfield, thence a horizontal line going left from that point to the vertical axis, which will give you your takeoff field length.
