That's right... the Canon uses a 1" sensor which is relatively large for a camera of this type, but limits the range of focal lengths possible.
The Lumix ZS70's 1/2.3" sensor is 28 sq. millimeters with 20 million pixel sites crowded onto it. That's more than 700,000 pixel sites per sq mm.
The Canon G9X's 1" sensor is more than 4X larger with 116 sq. mm. It's also a 20MP camera, so there are a little less than 173,000 pixel sites per sq mm.
Larger sensors that are less crowded and able to use bigger individual pixel sites generally make for better image quality. The larger sensor is less prone to heat build up and cross-talk between pixels, which makes for less "noise" in images, so can be used at higher ISOs to be able to shoot in lower light conditions. Large individual pixels also are generally able to capture more fine detail, which is more apparent with larger prints (or if more cropping is done to images). The Canon G9X has an ISO range of 125 to 12800 (expandable to 25600). The Lumix ZS70's ISO range is 80-3200 (expandable to 6400). In both cases, you might not find the highest avail. ISOs to give acceptable image quality (it's a subjective thing)... but basically the Canon camera has a two stop advantage, which means it should be possible to shoot in 1/4 the light level needed for the Panasonic.
Conversely, lens focal length range is more limited with larger apertures. To compare lenses on cameras a with a wide variety of different size sensors, we often use "35mm film/full frame" equivalents. In this case the Canon camera's zoom is equivalent to FF 28 to 84mm (it's actual focal length is 10.2-30.6mm, with the 2.7X "lens factor" of a 1" size sensor).... moderately wide angle to short telephoto. The Panasonic offers a much wider range, especially the telephoto end of it's zoom, with FF equivalent of 24 to 720mm (it's actual focal length is 4.3-129mm, with a 5.6X lens factor from the 1/2.3" size sensor).... slightly wider to much more powerful telephoto. This would typically make the Panasonic a better choice for small, distant subjects such as wildlife... so long as it's in good light.
Lens apertures are also different. The Canon's zoom has a fairly large, bright f/2 (wide) to 4.9 (tele) aperture. The Panasonic's zoom aperture is f/3.3 (wide) to f/6.4 (tele). Both cameras have image stabilization, to help reduce image blur from camera shake.... but it is MUCH more difficult to counteract movement with a powerful 720mm equivalent telephoto than it is with a very modest 84mm equivalent! (More crowded sensors are also more susceptible to camera shake.)
Functionally, the Canon G9X does not have a viewfinder. You have to rely upon the LCD screen on the rear to compose your images. That can be difficult to see in bright light. (Note: Canon G5X and G1X Mark III models have a built-in electronic viewfinder. Earlier G1X and G3 models can optionally be fitted with an EVF-DC1 or EVF-DC2 viewfinder. G9X and G7X models have no viewfinder nor any means of adding an optional one.)
The Panasonic ZS70 has a built-in electronic viewfinder, in addition to the LCD screen on the rear of the camera. Either can be used to compose images.
The G9X is smaller and lighter than the ZS70.
The ZS70 gets more shots per battery charge than the G9X.
You might find some other things informative here:
https://www.imaging-resource.com/cameras/canon/g9x-mark-ii/vs/panasonic/zs70/P.S. It doesn't really matter much whether you are looking at Canon G9X or G9X Mark II.... they are almost identical in all the above respects. The older model can still be found used... for about $20 less (big whoop!). Lens and sensor appear the same. The main difference is that the Mark II has been upgraded with a newer processor that allows it to have a bit faster overall performance.
https://www.imaging-resource.com/cameras/canon/g9x/vs/canon/g9x-mark-ii/AlohaJim wrote:
...An alternative would be the Sony RX100 MKIV with a 1"sensor and a max. 200m zoom.
PHRubin wrote:
or Lumix DC-ZS200 (1" sensor, 24-360mm lens)
Well sure... Either of those would be great if you don't mind spending $800 instead of $400!
Cos1 wrote:
Buy the Sony A6500...
Another good possibility.... only $1600 with 18-135mm zoom (27 to 203mm FF equivalent)... not to mention almost 4X the size and weight of the G9X!
(The problem with asking for recommendations on a forum is that you get them! Many folks are only too happy to recommend the camera THEY bought.... regardless what you were asking about.)
If you had that kind of money to spend...
...I'd point out the Canon G1X Mark III, which uses an even larger APS-C size sensor (similar to what the A6300 uses) AND has a built in electronic viewfinder, yet still is a relatively compact, non-interchangeable lens (equivalent to 24-70mm f/2.8-5.6), "point n shoot" camera... but costs a bit over $1000.
...Or the Canon G3X with EVF-DC1 Viewfinder combo on sale for $900 (reg. $1300)... 1" sensor, 24-600mm f/2.8-5.6 equivalent lens, hot shoe for accessory flash and more.