Learn Hardcore Spanish (Spain): Pongo el mapa en el bolsillo para no perderme. - I put the map in my pocket so I don’t get lost.

Because mapa is masculine. Several nouns ending in -a that come from Greek are masculine, e.g., el mapa, el problema, el sistema, el tema, el programa. So you must say el mapa and use the pronoun lo for it.

If I replace "el mapa" with a pronoun, is it "lo" or "le"?

Use lo: Lo pongo en el bolsillo.... Le is for indirect objects and, in Spain, sometimes for direct objects that are animate masculine persons (leísmo), but not for things like a map.

Why is it "pongo" and not "me pongo"?

Because poner (no pronoun) means “to put/place (something somewhere).” Ponerse (reflexive) means “to put something on yourself” or “to become (a state).”

Correct here: Pongo el mapa en el bolsillo.
Reflexive for clothing: Me pongo el abrigo.
Reflexive for states: Me pongo nervioso.

Is "pongo" irregular?

Yes. Poner has an irregular first-person singular in the present: yo pongo. The rest are regular in the present: tú pones, él/ella pone, nosotros ponemos, vosotros ponéis, ellos/ellas ponen.

Why is it "en el bolsillo" and not "al bolsillo"?

With verbs like poner, meter, guardar, you use en to express the final location (inside the pocket): poner/meter/guardar algo en el bolsillo. A marks direction more generally and isn’t used with poner here. With echar, you can hear echar algo al bolsillo in Spain (more casual: “chuck it in your pocket”). Poner al bolsillo sounds wrong.

Could I say "meter" or "guardar" instead of "poner"?

Yes, and they’re often more idiomatic for pockets in Spain:

Meto el mapa en el bolsillo. (put into)
Guardo el mapa en el bolsillo. (put away/keep) Poner is more general (“put/place”) but acceptable.

Should it be "mi bolsillo" instead of "el bolsillo"?

Not necessary. Spanish often uses the definite article with clothing/body parts when the possessor is clear: en el bolsillo naturally means “in my pocket.” Use mi if you need to specify or contrast: en mi bolsillo, no en el tuyo. You can also say en un bolsillo if it’s just “in a pocket (unspecified).”

Why is there no subject pronoun "yo"?

Spanish normally drops subject pronouns because the verb ending shows the subject. Pongo already means “I put.” Yo pongo is used only for emphasis or contrast.

What does "perderme" mean here, and how is it different from "perderlo" or "perderse"?

perderme = “to get lost (myself)” (reflexive/pronominal). Me pierdo = “I get lost.”
perderlo = “to lose it (the map)” (transitive). Lo pierdo = “I lose it.”
perderse can also mean “to miss out on” something: No quiero perderme el concierto. Here, given the map, the reading is “so I don’t get lost.”

Why is the pronoun attached to the infinitive: "para no perderme" and not "para no me perder"?

With an infinitive, object/reflexive pronouns attach to the end: perderme, perderlo, perdérmelo (note stress marks when needed). The negation no goes before the infinitive: para no perderme. If you use a conjugated verb, the pronoun goes before it: para que no me pierda.

Why use "para" and not "por"?

Para expresses purpose/goal (“in order to”): para no perderme = “so I don’t get lost.” Por generally expresses cause/reason/means; por no perderme would mean “because I don’t get lost,” which doesn’t fit here.

Could I say "para que no me pierda" instead?

Yes, it’s correct but different in structure:

Para no perderme = same subject as the main verb (I put it… so I don’t get lost).
Para que no me pierda uses a subordinate clause with the subjunctive. It’s especially natural when the subject changes: Lo pongo en el bolsillo para que tú no lo pierdas / para que no se me pierda.

Is "para que no me pierdo" ever correct?

No. After para que, you need the subjunctive: para que no me pierda. Using the indicative (me pierdo) there is incorrect.

Does "perder" change to "pierdo"? Why don’t we see it in "perderme"?

Yes, perder is a stem-changing verb (e→ie) in the present: pierdo, pierdes, pierde, perdemos, perdéis, pierden. You don’t see the change in perderme because it’s an infinitive; the change appears when conjugated: para que no me pierda.

What’s the difference between "bolsillo", "bolso", "bolsa" and "cartera"?

bolsillo = pocket (in clothing).
bolso = handbag/purse (Spain).
bolsa = bag (plastic/paper/shopping bag).
cartera = wallet (Spain; also “briefcase” in some contexts).

Does "pongo" mean “I’m putting (now)” or “I put (habitually)”?

Either. The Spanish present covers both current and habitual actions. Context tells you which. Alternatives:

Near future: Voy a meter/poner el mapa en el bolsillo.
Past: Puse el mapa en el bolsillo.

Is "Me pongo el mapa en el bolsillo" acceptable?

It sounds odd. Ponerse is mainly for clothing/accessories or states. For putting something into a pocket, use meter/guardar (or poner non‑reflexively): Me meto el mapa en el bolsillo / Guardo el mapa en el bolsillo.