"We all camp in the summer in Waiʻanae."
Translation:Hoʻomoana kākou i ke kau wela ma Waiʻanae.
i and ma are interchangeable in that they mean in,on, at or to. Furthermore they can give a feeling of motion. i ke kau wela is the direct object of the subject kakou. Ma Waiʻanae is the add on and gives a stationary feeling "at" some place an i at this position would give a feeling of motion to Waiʻanae
Historical Facts (Waiʻanae)
Because of Maui’s influence on the land and sea, the ancient people of Waianae became a prosperous fishing community. But by 1811, traders from Europe and America had entered the scene. They wanted the sandalwood trees that grew in Waianae, so the Hawaiian chiefs made everyone contribute to harvesting them. As a result, their crops were neglected. Contact with the foreigners also exposed the natives to outside diseases, and the local population plummeted.
In the late 1800s, various companies attempted to capitalize on the area’s lush land, and one businessman even built a railroad connecting Waianae to Honolulu. However, when the Waianae Sugar Plantation closed in 1946, all other commercialization efforts in the area ceased. Today, the West Coast of Oahu is one of the few places on the island untouched by modern industry, which has allowed the native wildlife to thrive.
Agree, they are basically interchangeable, but DL seems to be setting a pattern of using "ma" for locations and "i" for time, both of which are good choices, but not the only choices. You're also right in that "i" should be used to indicate motion toward (E hele ana mākou i Maui) and definitely (along with "iā") for indicating a direct object (Ua ʻai wau i ka poi). Which brings up another interesting point. Apparently DL refuses to accept "wau" as a variation of "au." When I used it in a sentence, I was told I had a "typo"! They may have been influenced by the text Ka Lei Haʻaheo which uses only "au," but basically everywhere else "wau" is accepted as a common variation of "au." (Maybe it will show up in a higher-level lesson that I haven't gotten to.)