This has definitely lead me down the right road, i ended up creating a splash screen which checks to see if the parameter is blank, if it is it proceeds to the default screen. If it is not it navigates to a subscreen and passes through the variable "loc" where i then use your coalesce method to determine once again if this variable is blank and if not it uses that as the locationid
URL I pass through:
<iframe width="1024px" height="768px" src="https://web.powerapps.com/webplayer/iframeapp?source=iframe&screenColor=rgba(104,101,171,1)&appId=/providers/Microsoft.PowerApps/apps/[App GUID]&LocationID=[Location GUID]"></iframe>
From splashscreen control i add a timer control and "OnTimeEnd":
If(Not(IsBlank(Param("LocationID"))),Navigate(SUM_Screen,ScreenTransition.Cover,{loc:Param("LocationID")}),Navigate(ACQ_Screen,ScreenTransition.Cover))
Then on the destination screen i filter the gallery as below:
SortByColumns(Filter('[dbo].[SummaryTask]', Coalesce(loc, LOC_Gallery.Selected.LocationID) = LocationID), "SortOrder")
One final question i have is what are the correct dimensions for a "Portrait" powerapp. when creating a landscape i can change between different preferred resolutions and it actually tells me what they are. for portrait i am having a hard time finding the correct setting for height and width, or at least the ratio of the two.